MAINT: act tool currently fails

[tylerjereddy]

Use of the act tool has been growing in the community to facilitate local iteration on CI testing for GitHub actions.

It almost succeeds with our current pydarshan-devel branch--the main test suite does pass for all Python versions it seems, but there is a failure later on:

| =========== 412 passed, 2 xfailed, 346 warnings in 403.52s (0:06:43) ===========
[Python Testing/test_pydarshan-9 ]   ✅  Success - Test with pytest
[Python Testing/test_pydarshan-9 ] ⭐  Run pyflakes check
[Python Testing/test_pydarshan-9 ]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /var/run/act/workflow/10] user= workdir=
[Python Testing/test_pydarshan-9 ]   ❌  Failure - pyflakes check
[Python Testing/test_pydarshan-9 ] exit with `FAILURE`: 1
Error: Job 'test_pydarshan' failed

May need to double check the robustness of the shell-style exit code handling in the pyflakes check section of CI control flow:

pyflakes darshan/backend | (grep -E -i 'assigned to but never used' || exit 0 && exit 123)