Install pytest-mypy-plugins on 3.13

Author: hynek

pyproject.toml

@@ -30,7 +30,7 @@ dynamic = ["version", "readme"]
 
 [project.optional-dependencies]
 tests-mypy = [
-  'pytest-mypy-plugins; platform_python_implementation == "CPython" and python_version >= "3.9" and python_version < "3.13"',
+  'pytest-mypy-plugins; platform_python_implementation == "CPython" and python_version >= "3.9"',
   # Since the mypy error messages keep changing, we have to keep updating this
   # pin.
   'mypy>=1.11.1; platform_python_implementation == "CPython" and python_version >= "3.9"',