Only run Test Report CI step on pushes to main

The test-reporter GitHub action doesn't work for public repos

.github/workflows/ci.yml

@@ -58,10 +58,8 @@ jobs:
         MIX_ENV: test
       run: mix test --exclude pending
     - name: Test Report
-      env:
-        MIX_ENV: test
       uses: dorny/test-reporter@v1
-      if: success() || failure()
+      if: (success() || failure()) && github.event_name == 'push'
       with:
         name: Mix Tests on Elixir ${{ matrix.elixir-version }} / OTP ${{ matrix.otp-version }}
         path: _build/test/lib/logger_json/test-junit-report.xml