Upgrade Guava to the latest version

[elefeint]

Spring Cloud GCP uses google-cloud-bom for the common dependencies. We have recently turned on Snyk vulnerability detection, and it found a deserialization issue with Guava 20.0.
The recommended remediation step is to upgrade to 24.1.1 or higher.

Would it be possible to upgrade Guava version in google-cloud-clients POM?

Spring Cloud GCP tracking issue: spring-attic/spring-cloud-gcp#1207

[sduskis]

@elharo, can you please chime in?

[garrettjonesgoogle]

A more recent version of grpc-java is using guava 26.0-android now, so we should bump to that.

[elharo]

I feel like we should upgrade everything or nothing. 26.0-android is likely strictly better but there's more than grpc to fix here.