Update entrypoint selection

[jrbourbeau]

Newer versions of Python and the importlib_metadata backport have deprecated get(...) in favor of .select(...). This helps avoid the following warning (xref this CI build)

 fsspec/__init__.py:49
  /home/runner/work/filesystem_spec/filesystem_spec/fsspec/__init__.py:49: DeprecationWarning: SelectableGroups dict interface is deprecated. Use select.
    for spec in entry_points.get("fsspec.specs", []):

[martindurant]

Bahh, this thing has changed too m many times! thanks for digging it out.