replace imghdr by puremagic

imghdr allowed to detect a few imagetimes and has been deprecated
in python 3.13: https://docs.python.org/3.12/library/imghdr.html

from the release notes:

> The filetype, puremagic, or python-magic libraries should be used as replacements.
> For example, the puremagic.what() function can be used to replace the imghdr.what()
> function for all file formats that were supported by imghdr.

See also https://github.com/cdgriffith/puremagic/blob/763349ec4d02ba930fb1142c6eb684afdf06c6ab/puremagic/main.py#L421

Author: bernt-matthias

lib/galaxy/dependencies/pinned-requirements.txt

@@ -133,6 +133,7 @@ propcache==0.2.0 ; python_version >= "3.8" and python_version < "3.13"
 prov==1.5.1 ; python_version >= "3.8" and python_version < "3.13"
 psutil==6.1.0 ; python_version >= "3.8" and python_version < "3.13"
 pulsar-galaxy-lib==0.15.6 ; python_version >= "3.8" and python_version < "3.13"
+puremagic==1.28 ; python_version >= "3.8" and python_version < "3.13"
 pycparser==2.22 ; python_version >= "3.8" and python_version < "3.13"
 pycryptodome==3.21.0 ; python_version >= "3.8" and python_version < "3.13"
 pydantic-core==2.23.4 ; python_version >= "3.8" and python_version < "3.13"

lib/galaxy/util/image_util.py

@@ -7,6 +7,8 @@
     Optional,
 )
 
+import puremagic
+
 try:
     from PIL import Image
 except ImportError:
@@ -26,7 +28,7 @@ def image_type(filename: str) -> Optional[str]:
             # exception we expect to happen frequently, so we're not logging
             pass
     if not fmt:
-        fmt = imghdr.what(filename)
+        fmt = puremagic.what(filename)
     if fmt:
         return fmt.upper()
     else: