ArrayAccess Compatibility

I found that offsetGet doesn't always return mixed, so leaving it as ReturnTypeWillChange for now

Author: Quazz

src/Config.php

@@ -62,22 +62,23 @@ private function merge(array $config)
         $this->config = array_replace($this->config, $config);
     }
 
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return isset($this->config[$offset]);
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->config[$offset];
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->config[$offset] = $value;
     }
 
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         unset($this->config[$offset]);
     }