`az functionapp config appsettings set` emits misleading "Invalid version: 21 for runtime java" warning on Linux Java 21/25 apps

## Title

`az functionapp config appsettings set` emits misleading "Invalid version: 21 for runtime java" warning on Linux Java 21/25 apps

## Describe the bug

When updating app settings on a Linux Java 21 (or Java 25) Function App on a Dedicated plan with a built-in Java image, every invocation of `az functionapp config appsettings set` prints a `WARNING: Invalid version: 21 for runtime java and os linux. Supported versions for runtime java and os linux are: ['25.0', '21.0', '17.0', '11.0', '8.0']. Run 'az functionapp list-runtimes' for more details on supported runtimes.`

The warning is **cosmetic** — the app settings update itself succeeds — but it is confusing to users and looks like a deployment-time error in CI logs.

The same kind of false positive can be reproduced on **.NET-isolated** apps when the Bicep/portal-stored runtime version is `8.0` (the Stacks API returns `"8"` for that runtime).

## Related command

```
az functionapp config appsettings set
```

(emitted by `check_language_runtime` → `_FunctionAppStackRuntimeHelper.resolve` in `appservice/custom.py`)

## Errors

```
PS C:\> az functionapp config appsettings set --name FA-demo-java-version --resource-group RG-demo-java-version --settings test_one=three
WARNING: Invalid version: 21 for runtime java and os linux. Supported versions for runtime java and os linux are: ['25.0', '21.0', '17.0', '11.0', '8.0']. Run 'az functionapp list-runtimes' for more details on supported runtimes.
[
...
]
```

## Issue script & Debug output

Repro:

1. Create a Linux Java 21 Function App on a Dedicated plan via the Portal (no other changes).
2. Run `az functionapp config appsettings set --name --resource-group --settings test_one=three --debug`.
3. Observe the warning above. The setting is still applied.

Tested with multiple `az` versions including the latest. The Portal stores the runtime as `Java|21` (no `.0` suffix); the Stacks API returns the version as `'21.0'`. The CLI's lookup table `old_to_new_version` in `_FunctionAppStackRuntimeHelper.resolve` does not have an entry for `21` (or `25`), so the version is reported as invalid even though Java 21 is fully supported.

## Expected behavior

No warning. `az functionapp config appsettings set` should treat `Java|21` as a valid configuration for a supported, available runtime.

More generally, the version normalization should not require a code change to add an entry every time a new Java/.NET major version ships.

## Environment Summary

```
azure-cli 2.85.0+ (also reproduces on previous releases)
core 2.85.0
```
(Reproduced internally on the latest GA and on at least one previous release.)

## Additional context

- Linux Java 21 Function App, Dedicated plan, built-in Java image.
- The warning text matches the API-returned versions exactly (`'25.0', '21.0', '17.0', '11.0', '8.0'`), confirming the API itself returned correct data — the validation logic in the CLI is what's wrong.
- For Web Apps, a related (but distinct) Java-versions issue was fixed by PR #32461. That PR was scoped to `_StackRuntimeHelper` (`az webapp list-runtimes`); the Functions counterpart `_FunctionAppStackRuntimeHelper.resolve` still uses a hardcoded version map.

A fix is in progress; will link the PR once filed.