Make pylibmagic import optional

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 data-data container which can use magic
just fine.

lib/galaxy/datatypes/sniff.py

@@ -37,7 +37,11 @@
 )
 from galaxy.util.path import StrPath
 
-import pylibmagic  # noqa: F401  # isort:skip
+try:
+    import pylibmagic  # noqa: F401  # isort:skip
+except ImportError:
+    # Not available in conda, but docker image contains libmagic
+    pass
 import magic  # isort:skip