mypy: disallow untyped defs by default (#11862)

Change our mypy configuration to disallow untyped defs by default, which ensures *new* files added to the code base are fully typed.

To avoid having to type-annotate everything now, add `# mypy: allow-untyped-defs` to files which are not fully type annotated yet.

As we fully type annotate those modules, we can then just remove that directive from the top.

testing/python/approx.py

@@ -1,3 +1,4 @@
+# mypy: allow-untyped-defs
 import operator
 from contextlib import contextmanager
 from decimal import Decimal

testing/python/collect.py

@@ -1,3 +1,4 @@
+# mypy: allow-untyped-defs
 import os
 import sys
 import textwrap

testing/python/fixtures.py

@@ -1,3 +1,4 @@
+# mypy: allow-untyped-defs
 import os
 import sys
 import textwrap
@@ -4403,7 +4404,7 @@ def test_fixture_named_request(pytester: Pytester) -> None:
     result.stdout.fnmatch_lines(
         [
             "*'request' is a reserved word for fixtures, use another name:",
-            "  *test_fixture_named_request.py:5",
+            "  *test_fixture_named_request.py:6",
         ]
     )
 

testing/python/integration.py

@@ -1,3 +1,4 @@
+# mypy: allow-untyped-defs
 import pytest
 from _pytest._code import getfslineno
 from _pytest.fixtures import getfixturemarker

testing/python/metafunc.py

@@ -1,3 +1,4 @@
+# mypy: allow-untyped-defs
 import dataclasses
 import itertools
 import re

testing/python/raises.py

@@ -1,3 +1,4 @@
+# mypy: allow-untyped-defs
 import re
 import sys