[dropbox] Re-enable tests on Python3.12

tests/test_dropbox.py

@@ -1,15 +1,7 @@
 import io
-import sys
 from datetime import datetime
-from unittest import SkipTest
 from unittest import mock
 
-if sys.version_info >= (3, 12, 0):
-    raise SkipTest(
-        "dropbox library does not support Python 3.12+. "
-        "Skipping all tests in test_dropbox.py"
-    )
-
 from django.core.exceptions import ImproperlyConfigured
 from django.core.exceptions import SuspiciousFileOperation
 from django.core.files.base import File