github/workflows: do not build scheduled unit tests for stable-23.0

This partly reverts commit 4e8c906.

It only makes sense to add stable branches to the scheduled builds once
they use the same setup as master. Otherwise CI breaks [1]. The setup
changed in labgrid-project#1079 which introduced separating labgrid/crossbar venvs and
moved the crossbar dependency to crossbar-requirements.txt. That means we
cannot add the stable branch to the scheduled CI tests until the stable
branch includes this setup, i.e. starting with stable-23.1.

The setup has no impact on the docker tests, so leave them enabled for
stable-23.0.

[1] https://github.com/labgrid-project/labgrid/actions/runs/5462091372

Signed-off-by: Bastian Krause <bst@pengutronix.de>

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

@@ -11,7 +11,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version: ['3.8', '3.9', '3.10', '3.11']
-        branch: ['master', 'stable-23.0']
+        branch: ['master']
     uses: ./.github/workflows/reusable-unit-tests.yml
     with:
       python-version: ${{ matrix.python-version }}