[12.x] Fix TestResponse::assertSessionMissing() when given an array of keys

PR #55763 remove `else` from `is_array($key)` condition which cause
regression bug to occur on existing application.

Signed-off-by: Mior Muhammad Zaki <[email protected]>

Author: crynobone

src/Illuminate/Testing/TestResponse.php

@@ -1670,6 +1670,8 @@ public function assertSessionMissing($key, $value = null)
             foreach ($key as $value) {
                 $this->assertSessionMissing($value);
             }
+
+            return $this;
         }
 
         if (is_null($value)) {