Texinfo in the GitHub OS X runners must be ancient. Even Texinfo 5.1
can handle UTF-8.
```
MAKEINFO /Users/runner/work/heimdal/heimdal/doc/heimdal.info
/Users/runner/work/heimdal/heimdal/doc/hx509.texi:11: warning: unrecognized encoding name `UTF-8'.
/Users/runner/work/heimdal/heimdal/doc/heimdal.texi:12: warning: unrecognized encoding name `UTF-8'.
/Users/runner/work/heimdal/heimdal/doc//setup.texi:380: Next field of node `Using soft aliases for configuring referrals' not pointed to (perhaps incorrect sectioning?).
/Users/runner/work/heimdal/heimdal/doc//setup.texi:404: This node (Checking the setup) has the bad Prev.
/Users/runner/work/heimdal/heimdal/doc//setup.texi:350: Prev field of node `Using hard aliases for realm migration' not pointed to.
/Users/runner/work/heimdal/heimdal/doc//setup.texi:310: This node (Using namespaces and synthetic principals to keep the database small) has the bad Next.
makeinfo: Removing output file `/Users/runner/work/heimdal/heimdal/doc/heimdal.info' due to errors; use --force to preserve.
make[1]: *** [/Users/runner/work/heimdal/heimdal/doc/heimdal.info] Error 1
```
- 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
