GitHub: Special builds for more branches

GitHub: Special builds for more branches

Instead of triggering scan-build builds on pushes to the `scan-build` branch,
or valgrind builds on pushes to the `valgrind` branch, let's have pushes to
branches matching `scan-build*` and `valgrind*` branch name globs trigger the
corresponding builds.

Do not forget to delete those branches when you're done!