Expect type stubs from canonicaljson (#14992)

* canonicaljson has stubs now

since https://github.com/matrix-org/python-canonicaljson/pull/52

which is included in the lockfile version we use for type checking.

* Changelog

changelog.d/14992.misc

@@ -0,0 +1 @@
+Improve type hints.

mypy.ini

@@ -142,9 +142,6 @@ disallow_untyped_defs = True
 [mypy-authlib.*]
 ignore_missing_imports = True
 
-[mypy-canonicaljson]
-ignore_missing_imports = True
-
 [mypy-ijson.*]
 ignore_missing_imports = True