Fix phpstan errors

Author: Sephster

Diff for: tests/Grant/AuthCodeGrantTest.php

@@ -509,7 +509,7 @@ public function testValidateAuthorizationRequestInvalidScopes(): void
             return;
         }
 
-        $this->fail('The expected exception was not thrown');
+        self::fail('The expected exception was not thrown');
     }
 
     public function testCompleteAuthorizationRequest(): void
@@ -594,7 +594,7 @@ public function testCompleteAuthorizationRequestDenied(): void
             return;
         }
 
-        $this->fail('The expected exception was not thrown');
+        self::fail('The expected exception was not thrown');
     }
 
     public function testRespondToAccessTokenRequest(): void

Diff for: tests/Grant/ImplicitGrantTest.php

@@ -241,7 +241,7 @@ public function testValidateAuthorizationRequestInvalidScopes(): void
             return;
         }
 
-        $this->fail('Did not throw expected exception');
+        self::fail('Did not throw expected exception');
     }
 
     public function testCompleteAuthorizationRequest(): void
@@ -310,7 +310,7 @@ public function testCompleteAuthorizationRequestDenied(): void
             return;
         }
 
-        $this->fail('Did not throw expected exception');
+        self::fail('Did not throw expected exception');
     }
 
     public function testAccessTokenRepositoryUniqueConstraintCheck(): void