Remove cover of not existing method

Author: Eremeev Ales

test/suite/unit/NotFoundResponseExceptionTest.php

@@ -14,7 +14,6 @@ class NotFoundResponseExceptionTest extends TestCase
 {
  /**
  * @covers ::__construct
- * @covers ::getMessage
  */
  public function testException(): void
  {

test/suite/unit/UnauthorizedResponseExceptionTest.php

@@ -14,7 +14,6 @@ class UnauthorizedResponseExceptionTest extends TestCase
 {
  /**
  * @covers ::__construct
- * @covers ::getMessage
  */
  public function testException(): void
  {

test/suite/unit/UnexpectedResponseExceptionTest.php

@@ -14,7 +14,6 @@ class UnexpectedResponseExceptionTest extends TestCase
 {
  /**
  * @covers ::__construct
- * @covers ::getMessage
  */
  public function testException(): void
  {