tests/test-check-pyflakes.t

run-tests: ignore PermissionError when checking available ports

I'm not sure what this is, but I'm getting it occasionally when running in WSL.
When it was raised, none of the tests could run.

#require test-repo pyflakes hg10

  $ . "$TESTDIR/helpers-testrepo.sh"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ cat > test.py <<EOF
  > print(undefinedname)
  > EOF
  $ "$PYTHON" -m pyflakes test.py 2>/dev/null | "$TESTDIR/filterpyflakes.py"
  test.py:1:* undefined name 'undefinedname' (glob)
  
  $ cd "`dirname "$TESTDIR"`"

  $ testrepohg locate 'set:**.py or grep("^#!.*python")' \
  > -X hgext/fsmonitor/pywatchman \
  > -X mercurial/pycompat.py -X contrib/python-zstandard \
  > -X mercurial/thirdparty \
  > 2>/dev/null \
  > | xargs "$PYTHON" -m pyflakes 2>/dev/null | "$TESTDIR/filterpyflakes.py"
  contrib/perf.py:*:* undefined name 'xrange' (glob) (?)
  mercurial/hgweb/server.py:*:* undefined name 'reload' (glob) (?)
  mercurial/util.py:*:* undefined name 'file' (glob) (?)
  mercurial/encoding.py:*:* undefined name 'localstr' (glob) (?)
  tests/run-tests.py:*:* undefined name 'PermissionError' (glob) (?)