Update actions/checkout@v3 to @v4

This gets rid of the warning "Node.js 16 actions are deprecated. Please
update the following actions to use Node.js 20: actions/checkout@v3. For
more information see:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/."

.github/workflows/bandit.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Bandit security check for code
         uses: akaihola/bandit-report-artifacts@use-config

.github/workflows/codespell.yml

@@ -8,5 +8,5 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: codespell-project/actions-codespell@master

.github/workflows/darker-flake8.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Run Darker's own GitHub action straight from the repository

.github/workflows/flake8.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: TrueBrain/actions-flake8@v2
         with:
           plugins: >

.github/workflows/help-in-readme.yml

@@ -5,7 +5,7 @@ jobs:
   help-in-readme:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - run: pip install '.[flynt,isort]'
       - name: Verify that README contains output of darker --help
         shell: python

.github/workflows/isort.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
       - run: pip install 'isort>=5.0.1'
       - uses: wearerequired/[email protected]

.github/workflows/mypy.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
       - run: |
           pip install -U \

.github/workflows/pylint.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
       - name: Install dependencies for running Pylint
         run: |

.github/workflows/python-package.yml

@@ -19,7 +19,7 @@ jobs:
     outputs:
       wheel-path: ${{ steps.get-darker-version.outputs.wheel-path }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
       - name: Install wheel
         run: python -m pip install wheel
@@ -54,7 +54,7 @@ jobs:
     needs:
       - build-wheel
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: cachix/install-nix-action@v22
         with:
           nix_path: nixpkgs=channel:nixos-unstable
@@ -104,7 +104,7 @@ jobs:
     needs:
       - build-wheel
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
           # need full history since Pytest runs Darker itself below
@@ -144,7 +144,7 @@ jobs:
     needs:
       - build-wheel
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
       - name: Install twine
         run: python -m pip install twine

.github/workflows/pyupgrade.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
       - run: pip install pyupgrade
       - name: Ensure modern Python style using pyupgrade

.github/workflows/safety.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
       - run: pip install -U pip-tools
       - run: pip-compile setup.cfg

.github/workflows/test-bump-version.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
 
       - name: Make sure that `bump_version.py` still finds all version strings

.github/workflows/test-future.yml

@@ -12,7 +12,7 @@ jobs:
   test-future:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           ref: 'master'
           fetch-depth: 0

.github/workflows/yaml-lint.yml

@@ -5,6 +5,6 @@ jobs:
   lintAllTheThings:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: yaml-lint
         uses: ibiqlik/action-yamllint@v3

README.rst

@@ -729,7 +729,7 @@ Create a file named ``.github/workflows/darker.yml`` inside your repository with
      lint:
        runs-on: ubuntu-latest
        steps:
-         - uses: actions/checkout@v3
+         - uses: actions/checkout@v4
            with:
              fetch-depth: 0 
          - uses: actions/setup-python@v5