[3.13] gh-133403: Run mypy on Tools/build/mypy.ini changes (GH-137692) (#137699)

(cherry picked from commit e93dca7)

Author: sobolevn

.github/workflows/mypy.yml

@@ -13,6 +13,7 @@ on:
       - "Lib/test/libregrtest/**"
       - "Lib/tomllib/**"
       - "Misc/mypy/**"
+      - "Tools/build/mypy.ini"
       - "Tools/build/check_extension_modules.py"
       - "Tools/build/compute-changes.py"
       - "Tools/build/deepfreeze.py"