Disallow untyped defs in `tests/test_util/test_util_images.py` (#13543)

Co-authored-by: Adam Turner <9087854+aa-turner@users.noreply.github.com>

pyproject.toml

@@ -290,7 +290,6 @@ module = [
     "tests.test_util.test_util",
     "tests.test_util.test_util_display",
     "tests.test_util.test_util_docutils",
-    "tests.test_util.test_util_images",
     "tests.test_util.test_util_inventory",
     # tests/test_writers
     "tests.test_writers.test_docutilsconf",

tests/test_util/test_util_images.py

@@ -11,13 +11,17 @@ from sphinx.util.images import (
     parse_data_uri,
 )
 
+TYPE_CHECKING = False
+if TYPE_CHECKING:
+    from pathlib import Path
+
 GIF_FILENAME = 'img.gif'
 PNG_FILENAME = 'img.png'
 PDF_FILENAME = 'img.pdf'
 TXT_FILENAME = 'index.txt'
 
 
-def test_get_image_size(rootdir):
+def test_get_image_size(rootdir: Path) -> None:
     assert get_image_size(rootdir / 'test-root' / GIF_FILENAME) == (200, 181)
     assert get_image_size(rootdir / 'test-root' / PNG_FILENAME) == (200, 181)
     assert get_image_size(rootdir / 'test-root' / PDF_FILENAME) is None