Downgrade version of pip due to a bug in version 21.1 (PR #2890)

# Description

Downgrade pip dependency due to bug: pypa/pip#9878

# Self Check:

- [ ] ~~Attached issue to pull request~~
- [x] Changelog entry
- [ ] ~~Type annotations are present~~
- [ ] ~~Code is clear and sufficiently documented~~
- [ ] ~~No (preventable) type errors (check using make mypy or make mypy-diff)~~
- [ ] ~~Sufficient test cases (reproduces the bug/tests the requested feature)~~
- [ ] ~~Correct, in line with design~~
- [ ] ~~End user documentation is included or an issue is created for end-user documentation (add ref to issue here: )~~

# Reviewer Checklist:

- [ ] Sufficient test cases (reproduces the bug/tests the requested feature)
- [ ] Code is clear and sufficiently documented
- [ ] Correct, in line with design

.github/dependabot.yml

@@ -15,3 +15,6 @@ updates:
       # Breaking change, see #2729 
     - dependency-name: "openapi-spec-validator"
       versions: [">=0.3.0"]
+      # version 21.1 contains a bug: https://github.com/pypa/pip/issues/9878
+    - dependency-name: "pip"
+      versions: [">=21.1"]

changelogs/unreleased/downgrade-pip-dependency.yml

@@ -0,0 +1,3 @@
+description: Downgrade version of pip due to a bug in version 21.1
+change-type: patch
+destination-branches: [master]

requirements.txt

@@ -12,7 +12,7 @@ jinja2==2.11.3
 more-itertools==8.7.0
 netifaces==0.10.9
 packaging==20.9
-pip==21.1
+pip==21.0.1
 ply==3.11
 pydantic==1.8.1
 pyformance==0.4