Pin importlib-metadata as flake8 metadata is wrong (#2447)
Pin importlib-metadata as flake8 metadata is wrong (#2447)

`importlib-metadata 5.0.0` breaks `flake8`, causing CI to fail.

`importlib` recommends constraining `importlib < 5` until flake8 adapts.

https://github.com/python/importlib_metadata/issues/406#issuecomment-1264666048
Parsl/parsl,Parsl/parsl,Parsl/parsl,Parsl/parsl