Cover runtime core tests on CI

Differential Revision: D49215928

fbshipit-source-id: 8f15546b5d6433693329c85bb1c1fc7761bb828a

Author: guangy10

.github/workflows/_unittest.yml

@@ -38,3 +38,5 @@ jobs:
         pip install .
         # Run pytest with coverage
         pytest --cov=./ --cov-report=xml
+        # Run gtest
+        /tmp/buck2 test runtime/core/... runtime/platform/...