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!
- s/build.yml/${build}.yml/ for the existing builds
- add filter on branches on push
- add scan-build build triggered by pushes to the scan-build branch or by PRs
that touch the scan-build.yml
- add valgrind build triggered by pushes to the valgrind branch or by PRs that
touch the valgrind.yml
