ci: use Python 3.11 from Debian 12 for testing

In commit 3ac7d39 ("buildworker,buildmaster: bump Debian to version
12") we switched the base system to Debian 12 which uses Python 3.11.2,
thus lets test on CI with same version.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

.github/workflows/build-push.yml

@@ -23,8 +23,7 @@ jobs:
  strategy:
  matrix:
  python-version:
- - "3.9"
- - "3.10"
+ - "3.11"
 
  steps:
  - name: Checkout