ci: add junit reporter

.github/workflows/build-test.yml

@@ -37,3 +37,13 @@ jobs:
 
       - name: run test
         run: opam exec -- dune runtest
+
+      - name: junit report
+        uses: dorny/test-reporter@v1
+        if: success() || failure() # run this step even if previous step failed
+        with:
+          name: Test Report
+          path: "_build/default/alcotest/test/*.xml,_build/default/junit/test/*.xml"
+          reporter: java-junit
+          fail-on-error: true
+          fail-on-empty: true # Use an empty test report to detect when something failed with the test runner