Merge remote-tracking branch 'origin/release-v1.33.2' into develop

changelog.d/9946.misc

+Unpin attrs dependency.

synapse/python_dependencies.py

@@ -79,7 +79,7 @@ REQUIREMENTS = [
     # Fedora 31 only has 19.1, so if we want to upgrade we should wait until 33
     # is out in November.)
     # Note: 21.1.0 broke `/sync`, see #9936
-    "attrs>=19.1.0,<21.1.0",
+    "attrs>=19.1.0,!=21.1.0",
     "netaddr>=0.7.18",
     "Jinja2>=2.9",
     "bleach>=1.4.3",