FIX: Fix type and default for argument of new testing helper.

Author: DWesl

lib/matplotlib/testing/__init__.py

@@ -53,7 +53,7 @@ def setup():
 def subprocess_run_for_testing(
         command: "list[str]",
         env: "dict[str, str]",
-        timeout=float,
+        timeout: float = None,
         stdout=None,
         stderr=None,
         check=False,