Upgrade deprecated pkg_resources

[AngelOnFira]

Locally, I'm running tests and getting deprecation warnings for the use of pkg_resources. According to this post:

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Use of pkg_resources is deprecated in favor of importlib.resources, importlib.metadata and their backports (importlib_resources, importlib_metadata). Users should refrain from new usage of pkg_resources and should work to port to importlib-based solutions.

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This PR makes the changes to follow the deprecation notice.

[AngelOnFira]

Note; this package uses CoreApi, and it also uses pkg_resources. However, that repo is archived, so I can't upstream a PR there.

[tahme]

Note that importlib.metadata is only available for Python >= 3.8 so older versions need to use the backported importlib_metadata package or keep using pkg_resources, like here:
https://github.com/pyscaffold/pyscaffold/pull/318/files#diff-832c6d0841c720713101f1313509d4255dacb74d3cc2c58f05cbe52c53de53ee