ci: generate CI job matrix from Python script

Closes #637

Co-authored-by: Yves Delley <burnpanck@users.noreply.github.com>

Author: mpusz

.flake8

@@ -9,6 +9,3 @@ ignore =
     E203,
     # line break before binary operator
     W503
-per-file-ignores =
-    # flake8 is just plain wrong here, contradicting black
-    .github/generate-job-matrix.py:E225,E231