[tooling] Ignore git-ignored files in shell-lint

[the-glu]

This PR fixes #1427 by excluding files that are excluded by git ignore files in the shell lint command.

Diffing the file list before & after the extra filter show expected results:

*** /tmp/b      2026-04-20 09:58:38.074510445 +0200
--- /tmp/a      2026-04-20 09:58:28.231460147 +0200
***************
*** 29,36 ****
  ./schemas/manage_type_schemas.sh
  ./github_pages/make_site_content.sh
  ./test/repo_hygiene/repo_hygiene.sh
- ./.venv/lib/python3.13/site-packages/nodejs_wheel/lib/node_modules/npm/lib/utils/completion.sh
- ./.venv/lib/python3.13/site-packages/nodejs_wheel/lib/node_modules/npm/node_modules/node-gyp/macOS_Catalina_acid_test.sh
  ./build/build_and_push.sh
  ./build/dev/startup/core_service.sh
  ./build/dev/run_locally.sh
--- 29,34 ----
***************
*** 38,41 ****
  ./scripts/git/version.sh
  ./scripts/git/commit.sh
  ./scripts/tag.sh
- 
--- 36,38 ----

[mickmis]

Do the same for dss https://github.com/interuss/dss/blob/master/Makefile#L95?

[the-glu]

Do the same for dss https://github.com/interuss/dss/blob/master/Makefile#L95?

Good idea, done there: interuss/dss#1443