roachtest: cluster_creation failed

roachtest.cluster_creation [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21516917?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21516917?buildTab=artifacts#/sqlsmith/setup=seed-multi-region/setting=multi-region) on release-25.4.17-rc @ [3981ecae25dbf445f122d375bf813b8859158a14](https://github.com/cockroachdb/cockroach/commits/3981ecae25dbf445f122d375bf813b8859158a14):

```
test sqlsmith/setup=seed-multi-region/setting=multi-region failed: (test_runner.go:901).func4: in provider: gce: T2A instances are not supported outside of [asia-southeast1-b,asia-southeast1-c,europe-west4-a,europe-west4-b,europe-west4-c,us-central1-a,us-central1-b,us-central1-f] [owner=test-eng]
```

Parameters:
- cloud=gce
- coverageBuild=false
- cpu=4
- runtimeAssertionsBuild=false
- ssd=0
Help

See: [roachtest README](https://github.com/cockroachdb/cockroach/blob/master/pkg/cmd/roachtest/README.md)

See: [How To Investigate \(internal\)](https://cockroachlabs.atlassian.net/l/c/SSSBr8c7)

Same failure on other branches

- #174930 roachtest: cluster_creation failed [O-roachtest O-robot T-testeng X-infra-flake branch-master]
- #174639 roachtest: cluster_creation failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-25.2.24-rc]
- #174597 roachtest: cluster_creation failed [O-roachtest O-robot T-testeng X-infra-flake branch-master]
- #174596 roachtest: cluster_creation failed [O-roachtest O-robot T-testeng X-infra-flake branch-master]

/cc @cockroachlabs/test-eng

[This test on roachdash](https://roachdash.crdb.dev/?filter=status:open%20t:.*cluster_creation.*&sort=title+created&display=lastcommented+project) | [Improve this report!](https://github.com/cockroachdb/cockroach/tree/master/pkg/cmd/bazci/githubpost/issues)

Start with the linked TeamCity log and artifacts, then read pkg/cmd/roachtest/README.md and compare the related cluster_creation failures listed in this issue. Confirm why the GCE test requests an unsupported T2A zone and identify the change or configuration needed for the test to complete successfully.

Written by the indexing model from the issue text.