[CI][NFC] Make lint for commits in PR change only (#6722)

Make lint for commits in PR change only not taking into account sycl
branch HEAD. Should fix issues like in
#6705 where lint reported errors for
files not affected in PR. To overcome current PRs stuck because of this
they need to use ignore-lint tag until PR will be based on devops
directory changes made here.

Author: apstasen

devops/actions/clang-format/action.yml

@@ -7,8 +7,7 @@ runs:
     shell: bash {0}
     run: |
       git config --global --add safe.directory /__w/llvm/llvm
-      git fetch origin sycl
-      git clang-format ${GITHUB_SHA}
+      git clang-format ${{ github.event.pull_request.base.sha }}
       git diff > ./clang-format.patch
   # Add patch with formatting fixes to CI job artifacts
   - uses: actions/upload-artifact@v1