GH Actions: local-macos-nohomebrew fails

[mkoeppe]

... because we set a too ambitious version number:

  [sage_docbuild-9.1.rc4-74948-gb249c4750f]     File "/Users/runner/work/sage/sage/.tox/local-macos-nobootstrap-minimal/local/lib/python3.9/site-packages/setuptools/config.py", line 548, in _parse_version
  [sage_docbuild-9.1.rc4-74948-gb249c4750f]       raise DistutilsOptionError(tmpl.format(**locals()))
  [sage_docbuild-9.1.rc4-74948-gb249c4750f]   distutils.errors.DistutilsOptionError: Version loaded from file: VERSION.txt does not comply with PEP 440: 9.1.rc4-74948-gb249c4750f
  [sage_docbuild-9.1.rc4-74948-gb249c4750f]   *

[dimpase]

we probably need to overhaul Homebrew actions quite a bit. There are various obsolete things, e.g. a macOS version is 11.0 instead of 11, something funny with an old version 11.7 of xcode, etc...

It seems to me that Homebrew packages need explicit installation, too.

[mkoeppe]

Also, homebrew has recently (again!) broken their python3. Because they hardcode the path to the SDK sysroot, it only works when the current Xcode command line tools are installed

[jhpalmieri]

Is this why cython is failing to compile with messages like

  clang: warning: no such sysroot directory: '/Library/Developer/CommandLineTools/SDKs/MacOSX11.sdk' [-Wmissing-sysroot]

(Failing with homebrew's Python 3, builds okay with /usr/bin/python3.)

[mkoeppe]

Yes, this is the symptom after a recent upgrade of homebrew.

[chapoton]

bump to 9.6