chore: Re-enable Ubuntu tests in CI.

Author: BenHenning

.github/workflows/test.yml

@@ -21,7 +21,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-latest]
+        os: [ubuntu-latest, macos-latest]
 
     steps:
       - name: Checkout experimentation plugin