Revert frozendict restriction, because we don't have issue with 2.3.5 version.
This is related to upstream PR https://github.com/matrix-org/synapse/pull/15114

--- a/pyproject.toml
+++ b/pyproject.toml
@@ -154,9 +154,7 @@ python = "^3.7.1"
 # we use the TYPE_CHECKER.redefine method added in jsonschema 3.0.0
 jsonschema = ">=3.0.0"
 # frozendict 2.1.2 is broken on Debian 10: https://github.com/Marco-Sulla/python-frozendict/issues/41
-# We cannot test our wheels against the 2.3.5 release in CI. Putting in an upper bound for this
-# because frozendict has been more trouble than it's worth; we would like to move to immutabledict.
-frozendict = ">=1,!=2.1.2,<2.3.5"
+frozendict = ">=1,!=2.1.2"
 # We require 2.1.0 or higher for type hints. Previous guard was >= 1.1.0
 unpaddedbase64 = ">=2.1.0"
 # We require 1.5.0 to work around an issue when running against the C implementation of