.github/workflows/scheduled-unit-tests: drop scheduled docker tests o…

…n stable-23.0

Adding the stable branches here is problematic: GitHub uses the workflow
definitions from the default branch (master). The workflow might not
match the stable branch. So drop it here.

As a replacement, the current stable branch is tested on a labgrid fork
that has the stable branch set as its default branch, so the workflow
is maintained in the same branch as the code.

Signed-off-by: Bastian Krause <[email protected]>

.github/workflows/scheduled-unit-tests.yml

@@ -21,7 +21,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        branch: ['master', 'stable-23.0']
+        branch: ['master']
     uses: ./.github/workflows/reusable-unit-tests-docker.yml
     with:
       branch: ${{ matrix.branch }}