[24.1] Make pylibmagic import optional

[mvdbeek]

I was trying to use the galaxy-data container for data source tools, but it fails with:

Traceback (most recent call last):
  File "/Users/mvandenb/src/galaxy/test/functional/tools/data_source.py", line 13, in <module>
    from galaxy.datatypes import sniff
  File "/usr/local/lib/python3.12/site-packages/galaxy/datatypes/sniff.py", line 40, in <module>
    import pylibmagic  # noqa: F401  # isort:skip
    ^^^^^^^^^^^^^^^^^
ModuleNotFoundError: No module named 'pylibmagic'

pylibmagic is just shipping the magic library and adds it to path, but that's not needed for the conda-package which installs libmagic (https://github.com/conda-forge/python-magic-feedstock/blob/main/recipe/meta.yaml)

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.