[5.x] Fix carbon deprecation warning

[jasonvarga]

Fixes #11553

This is already fixed in v6 but this backports it.

Context:

try {
    return Carbon::createFromFormat($this->saveFormat(), $value);
} catch (InvalidFormatException|InvalidArgumentException $e) {
    return Carbon::parse($value);
}

Sometimes $value is already a Carbon instance.
When you pass a Carbon instance to createFromFormat, you get an InvalidFormatException.
The catch will catch it, and pass the Carbon instance into parse, which just returns the instance back and logs the deprecation warning. We can avoid all that by just returning a Carbon instance early.