roachtest: fix hibernate nightly test

The previous version fails during installation with:
```
FAILURE: Build completed with 2 failures.

1: Task failed with an exception.
-----------
* What went wrong:
Execution failed for task ':hibernate-core:generateGraphParser'.
> Failed to load cache entry 7ed5a08bcdbd74c9347d61047c20a896 for task ':hibernate-core:generateGraphParser': Could not load from remote cache: Not in GZIP format

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Get more help at https://help.gradle.org.
==============================================================================

2: Task failed with an exception.
-----------
* What went wrong:
Execution failed for task ':hibernate-jpamodelgen:jaxb'.
> Failed to load cache entry dd3fbbdea5c65a87fb9d720c326dd64b for task ':hibernate-jpamodelgen:jaxb': Could not load from remote cache: Not in GZIP format

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Get more help at https://help.gradle.org.
==============================================================================
```

Release note: None

Author: rafiss

pkg/cmd/roachtest/tests/hibernate.go

@@ -23,7 +23,7 @@ var hibernateReleaseTagRegex = regexp.MustCompile(`^(?P<major>\d+)\.(?P<minor>\d
 
 // WARNING: DO NOT MODIFY the name of the below constant/variable without approval from the docs team.
 // This is used by docs automation to produce a list of supported versions for ORM's.
-var supportedHibernateTag = "6.6.0"
+var supportedHibernateTag = "6.6.20"
 
 type hibernateOptions struct {
 	testName string