ref: add mypy plugin to typing codeowners (#53709)

<!-- Describe your PR here. -->

.github/CODEOWNERS

@@ -74,8 +74,9 @@ Makefile                                                 @getsentry/owners-sentr
 .pre-commit-config.yaml                                  @getsentry/owners-sentry-dev
 .git-blame-ignore-revs                                   @getsentry/owners-sentry-dev
 
-mypy.ini                                                 @getsentry/python-typing
 /fixtures/stubs-for-mypy                                 @getsentry/python-typing
+/tools/mypy_helpers/                                     @getsentry/python-typing
+/tests/tools/mypy_helpers                                @getsentry/python-typing
 
 # GitHub Routing Automations - notion.so/473791bae5bf43399d46093050b77bf0
 /.github/labels.yml                                      @getsentry/open-source