Fix public-symbols-check workflow generation (open-telemetry#2876)

Consider only pull request events when running  public-symbols-check.

Author: xrmx

.github/workflows/generate_workflows_lib/src/generate_workflows_lib/misc.yml.j2

@@ -28,7 +28,7 @@ jobs:
     {%- if job_data == "public-symbols-check" %}
     if: |
       !contains(github.event.pull_request.labels.*.name, 'Approve Public API check')
-      && github.actor != 'opentelemetrybot'
+      && github.actor != 'opentelemetrybot' && github.event_name == 'pull_request'
     {%- endif %}
     steps:
       - name: Checkout repo @ SHA - ${% raw %}{{ github.sha }}{% endraw %}