Add ReturnTypeWillChange annotation

Author: iggyvolz

src/Map.php

@@ -798,6 +798,7 @@ public function offsetExists($offset)
      *
      * @see \JsonSerializable
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return (object) $this->toArray();

src/Pair.php

@@ -142,6 +142,7 @@ public function toArray(): array
      *
      * @psalm-return array{key: TKey, value: TValue}
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->toArray();

src/Traits/GenericCollection.php

@@ -27,6 +27,7 @@ public function isEmpty(): bool
      *
      * @see \JsonSerializable
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->toArray();