[6.x] Removed $value instanceof Carbon redundancy (#30932)

`Illuminate\Support\Carbon extends \Carbon\Carbon implements \Carbon\CarbonInterface`

src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php

@@ -773,7 +773,7 @@ protected function asDateTime($value)
         // If this value is already a Carbon instance, we shall just return it as is.
         // This prevents us having to re-instantiate a Carbon instance when we know
         // it already is one, which wouldn't be fulfilled by the DateTime check.
-        if ($value instanceof Carbon || $value instanceof CarbonInterface) {
+        if ($value instanceof CarbonInterface) {
             return Date::instance($value);
         }