fix: python 3.10 compatibility

retry of !22 (merged)

funkwhale_cli/utils.py

-import collections
 import json
+import sys
 import urllib.parse
 
 import pathvalidate
 
+if sys.version_info >= (3, 10):
+    from collections.abc import MutableMapping
+else:
+    from collections import MutableMapping
 
 def recursive_getattr(obj, key, permissive=False):
     """
@@ -92,7 +96,7 @@ def flatten(d, parent_key="", sep="_"):
     items = []
     for k, v in d.items():
         new_key = parent_key + sep + k if parent_key else k
-        if isinstance(v, collections.MutableMapping):
+        if isinstance(v, MutableMapping):
             items.extend(flatten(v, new_key, sep=sep).items())
         else:
             items.append((new_key, v))