test: clear super globals after testing

The following test failed. It depends global state.
1) CodeIgniter\HTTP\ResponseTest::testSetLink
Failed asserting that two strings are identical.

Author: kenjis

tests/system/Filters/InvalidCharsTest.php

@@ -46,6 +46,15 @@ protected function setUp(): void
         $this->invalidChars = new InvalidChars();
     }
 
+    protected function tearDown(): void
+    {
+        parent::tearDown();
+
+        $_GET    = [];
+        $_POST   = [];
+        $_COOKIE = [];
+    }
+
     private function createRequest(): IncomingRequest
     {
         $config    = new MockAppConfig();