GCSAuthManager does not seem to support credentials refresh - jobs crash mid

### Apache Iceberg version

1.10.1 (latest release)

### Query engine

Spark

### Please describe the bug 🐞

```
Caused by: java.lang.IllegalStateException: OAuth2Credentials instance does not support refreshing the access token. An instance with a new access token should be used, or a derived type that supports refreshing.
```

Getting this at some mid point of our job, after running for a few hours. Using GCSAuthManager. We assumed it would support credential refresh :/

@talatuyarer

### Willingness to contribute

- [ ] I can contribute a fix for this bug independently
- [ ] I would be willing to contribute a fix for this bug with guidance from the Iceberg community
- [ ] I cannot contribute a fix for this bug at this time

Start by tracing GCSAuthManager and how it creates or supplies credentials for a long-running Spark job. Reproduce the failure after the access token expires and inspect the OAuth2Credentials exception. Done means credential refresh works throughout the job without the reported IllegalStateException.

Written by the indexing model from the issue text.