ci: authenticate the cpp-linter API requests

--files-changed-only makes cpp-linter query the commit through the REST
API. With no token it uses the anonymous budget, which is 60 requests per
hour shared across every job on the runner's IP, so it fails outright
whenever that is already spent:

  response returned 403 from GET .../commits/10568eedaac4
  API rate limit exceeded for 52.150.29.102.

cpp_linter/rest_api/github_api.py reads GITHUB_TOKEN and sends it as an
Authorization header, which puts the request on this repository's own
budget instead.

Author: pvelesko

.github/workflows/clang-tidy-format.yml

@@ -21,6 +21,15 @@ jobs:
         with:
           submodules: recursive
       - name: Run C/C++ Linter
+        env:
+          # --files-changed-only makes cpp-linter ask the API which lines the
+          # commit touched. Unauthenticated it shares the 60/hour anonymous
+          # budget for the whole runner IP, which other jobs routinely exhaust:
+          #   response returned 403 from GET .../commits/<sha>
+          #   API rate limit exceeded for 52.150.29.102.
+          # cpp_linter/rest_api/github_api.py sends this as an Authorization
+          # header when set, moving the request onto the repo's own budget.
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           ml StdEnv
           . /home/chipStarUser/venv/bin/activate