Fix return type deprecation since Symfony 7.x

Method "Symfony\Component\Serializer\Encoder\DecoderInterface::decode()" might add "mixed" as a native return type declaration in the future. Do the same in implementation "Ang3\Component\Serializer\Encoder\ExcelEncoder" now to avoid errors or add an explicit @return annotation to suppress this message.

Author: JoryHogeveen

src/ExcelEncoder.php

@@ -227,7 +227,7 @@ public function supportsDecoding($format): bool
      * @throws RuntimeException           When data reading failed
      * @throws PhpSpreadsheetException    On data failure
      */
-    public function decode($data, $format, array $context = [])
+    public function decode($data, $format, array $context = []): mixed
     {
         if (!\is_scalar($data)) {
             throw new NotEncodableValueException(sprintf('Expected data of type scalar, %s given', \gettype($data)));