* tests: add apk release signing regression test

* buildmaster: build apk 3.0.5 from the OpenWrt sources mirror
* ci: run black in --check mode
* phase2: reformat master.cfg with black 26.10.1
* phase1: reformat master.cfg with black 26.10.1
* ci: bump lint tools and use `ruff check`
* ci: run test-lint on Python 3.13
* docker: upgrade base images to debian:13
* phase2: fix not signing each package
* CI(deps): Bump docker/metadata-action from 5 to 6
* phase2: don't sign each package
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