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
We should split build.yml into separate workflows for each OS, that way
we can have Windows builds triggered by changes to NTMakefiles, but not
Linux builds.
