Rails7 deployment to GAE Flex fails: Your runtime version for ruby is past End of Support.

Googlers: see b/365178099.

I've noticed in both MySQL and PostgreS tutorials, that when you follow the tutorial for https://cloud.google.com/ruby/rails/using-cloudsql-postgres (for instance), it fails at the step

`gcloud app deploy`

And the failure carries this error:

```
╔════════════════════════════════════════════════════════════╗
╠═ Uploading 2777 files to Google Cloud Storage ═╣
╚════════════════════════════════════════════════════════════╝
File upload done.
ERROR: (gcloud.app.deploy) INVALID_ARGUMENT: Error(s) encountered validating runtime. Your runtime version for ruby is past End of Support. Please upgrade to the latest runtime version available..
- '@type': [type.googleapis.com/google.rpc.DebugInfo](http://type.googleapis.com/google.rpc.DebugInfo)
detail: '[ORIGINAL ERROR] generic::invalid_argument: com.google.net.rpc3.RpcException:
generic::INVALID_ARGUMENT: Error(s) encountered validating runtime. Your runtime
version for ruby is past End of Support. Please upgrade to the latest runtime
version available.. [google.rpc.error_details_ext] { code: 3 message: "Error(s)
encountered validating runtime. Your runtime version for ruby is past End of Support.
Please upgrade to the latest runtime version available.." }'
```

Looking at latest rubies supported by Flex, I noticed that you should use 3.2 or 3.3 which in turn are warranted just by ubuntu22. So as not obvious at it may sound, a neat solution is to add this to app.yaml:

```
runtime: ruby
env: flex

# Yup, this part enforces ruby 3.2/3.3 and then the error disappears
runtime_config:
operating_system: "ubuntu22"
```

## Note

I havent tried the same with Mysql but I'm pretty sure the bug is also there.

Start with the Rails Cloud SQL PostgreSQL tutorial and its app.yaml, then compare the corresponding MySQL tutorial configuration. Reproduce the failure with gcloud app deploy and verify that the runtime configuration uses a supported Ubuntu 22 environment; done means both tutorials deploy successfully without the end-of-support error.

Written by the indexing model from the issue text.