[12.x] Ensure custom validation messages work for the File rule

[jackbayliss]

When using the File rule with custom messages for multiple files in the same request, the wrong message can appear. The generic file message is shown instead of the sub-rule messages (max, size, etc.). - This appears to be introduced by my previous PR - #57356

This PR resolves that and adds a test to prevent regression - I believe only File is affected because it wraps multiple sub-rules and has a default class-based file message. I've tried to same with Password, etc, and have been unable to get it to happen.

The alternative- if this feels too narrow could be:

-        if ($this->getAttributeType($attribute) !== 'file') {
+       if (class_exists($lowerRule) && ! is_subclass_of($lowerRule, DataAwareRule::class)) {

Any suggestions, please let me know 🫡 - Thanks!!

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