GitHub CI: ignore upload failure after build fails

We have the GitHub CI set up to upload the binaries generated by a
failed build.  This is intended to help people debug test failures, but
when the compilation fails there is no binary to upload.  In that case,
GitHub gets distracted by the upload failure and doesn't automatically
jump to the relevant failure.

Reconfigure the upload step to ignore errors due to file not found.

.github/workflows/matrix.yml

@@ -145,8 +145,9 @@ jobs:
     - name: build and test
       run: bash ./build-scripts/build.sh
     - name: upload artifacts if failed
-      uses: actions/upload-artifact@v1
+      uses: actions/upload-artifact@v2
       if: failure()
       with:
         name: cata_test
         path: tests/cata_test
+        if-no-files-found: ignore