[Kokoro] Invalid JWT signatures in GraalVM B and Integration jobs

[diegomarquezp]

ERROR: (gcloud.auth.activate-service-account) There was a problem refreshing your current auth tokens: invalid_grant: Invalid JWT Signature.

Occurs in GraalVM B and Integration Kokoro checks.
Marking these checks as non-required for the time being.

Originally posted by @diegomarquezp in #2288 (comment)

[diegomarquezp]

Example": https://btx.cloud.google.com/invocations/31d6ed11-73be-451d-8565-c59eda41ab60/targets/cloud-devrel%2Fclient-libraries%2Fjava%2Fjava-firestore%2Fpresubmit%2Fgraalvm-native-b/log