gh-101100: Fix Sphinx warning in gc.rst and refactor docs clean list (#103116)

Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>

Doc/tools/touch-clean-files.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+"""
+Touch files that must pass Sphinx nit-picky mode
+so they are rebuilt and we can catch regressions.
+"""
+
+from pathlib import Path
+
+# Input file has blank line between entries to reduce merge conflicts
+with Path("Doc/tools/clean-files.txt").open() as clean_files:
+    CLEAN = [
+        Path(filename.strip())
+        for filename in clean_files
+        if filename.strip() and not filename.startswith("#")
+    ]
+
+print("Touching:")
+for filename in CLEAN:
+    print(filename)
+    filename.touch()