tests/test-gendoc-pt_BR.t

extensions: load help from hgext.__index__ as a fallback this time

Prior to 843418dc0b1b, `hgext.__index__` was consulted first if present, which
caused the longer help from the extension modules to be ignored, even when
available.  But that change causes a bunch of test failures when the pyoxidized
binary bundles *.pyc in the binary, saying the there's no help topic for
`hg help $disabled_extension` and suggesting the use of `--keyword`, rather than
showing a summary and indicating that it is disabled.  Current failures were in
test-check-help.t, test-extension.t, test-help.t, and test-qrecord.t.

Ideally, we would read the various *.pyc files from memory and slurp in the
docstring, but I know that they used to not be readable as resources, and I
can't figure out how to make it work now.  So maybe 3.9 and/or the current
PyOxidizer doesn't support it yet.  I got closer in py2exe with
`importlib.resources.open_binary("hgext", "rebase.pyc")`, but `open_binary()` on
*.pyc fails in pyoxidizer.[1]  Either way, the *.pyc can't be passed to
`ast.parse()` as `extensions._disabledcmdtable()` is doing, so I'm setting that
aside for now.

[1] https://github.com/indygreg/PyOxidizer/issues/649

#require docutils gettext

  $ $TESTDIR/check-gendoc pt_BR
  checking for parse errors