feat: upload artifacts from visual comparison for inspection

It allows evaluating whether the visual differences are acceptable
The condition in step description ensures that the artifacts are not uploaded on cancelled builds

.github/workflows/main.yml

@@ -52,3 +52,11 @@ jobs:
         run: bundle exec rake compile
       - name: run the tests
         run: bundle exec rspec
+        id: test
+      - name: upload test artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: "visual-matching-results-ruby-${{ matrix.ruby}}"
+          path: 'tmp/reference-image-matches'
+          if-no-files-found: ignore
+        if: success() || steps.test.conclusion == 'failure'