ci: run downstream native image tests (#779)

* ci: running downstream native image tests

* docs: updated comments

Author: suztomo

.github/workflows/downstream-native-image.yaml

@@ -7,15 +7,15 @@ on:
 # Keeping this file separate as the dependencies check would use more
 # repositories than needed this downstream check for GraalVM native image
 # compilation.
-name: downstream
+name: downstream-native-image
 jobs:
   # GraalVM job ensures the compatibility of GraaVM version
   graalvm:
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
-        graalvm: [22.1.0]
+        graalvm: [22.1.0, 22.0.0.2, 21.3.2]
         java: [11, 17]
         repo:
           # GAPIC library that doesn't use a real GCP project in integration tests

.kokoro/downstream-client-library-check.sh

@@ -62,5 +62,9 @@ if [[ $CLIENT_LIBRARY == "bigtable" ]]; then
   popd
 fi
 
+# We don't want to fail the test due to enforcer rule, before running GraalVM
+# tests. Checking GraalVM buidl result is more important.
+export INTEGRATION_TEST_ARGS="-Denforcer.skip=true"
+
 # This reads the JOB_TYPE environmental variable ("test" or "graalvm")
 .kokoro/build.sh