Fix CI: allow coverage comment to fail for Dependabot PRs

Dependabot PRs don't have permission to post PR comments, which was
causing the build-and-test job to fail even though all tests passed.
Adding continue-on-error to make this step non-blocking.

Author: mliotta

.github/workflows/ci.yml

@@ -61,6 +61,7 @@ jobs:
       - name: Add coverage PR comment
         uses: marocchino/sticky-pull-request-comment@v2
         if: github.event_name == 'pull_request'
+        continue-on-error: true  # Dependabot PRs don't have permission to post comments
         with:
           recreate: true
           path: coverage/report/SummaryGithub.md