[11.x] Fix missing return $this for assertOnlyJsonValidationErrors

[LeTamanoir]

The assertOnlyJsonValidationErrors does not return $this even though it is type hinted to return $this.

framework/src/Illuminate/Testing/TestResponse.php

Lines 979 to 997 in 32bbb68

	/**
	* Assert that the response has the given JSON validation errors but does not have any other JSON validation errors.
	*
	* @param string|array $errors
	* @param string $responseKey
	* @return $this
	*/
	public function assertOnlyJsonValidationErrors($errors, $responseKey = 'errors')
	{
	$this->assertJsonValidationErrors($errors, $responseKey);
	$jsonErrors = Arr::get($this->json(), $responseKey) ?? [];
	$expectedErrorKeys = collect($errors)->map(fn ($value, $key) => is_int($key) ? $value : $key)->all();
	$unexpectedErrorKeys = Arr::except($jsonErrors, $expectedErrorKeys);
	PHPUnit::withResponse($this)->assertTrue(count($unexpectedErrorKeys) === 0, 'Response has unexpected validation errors: '.collect($unexpectedErrorKeys)->keys()->map(fn ($key) => "'{$key}'")->join(', '));
	}