Fix example to avoid fatal error

[robocoder]

With PHP 8.x, the first example b0rks:

PHP Fatal error:  Uncaught Error: Firebase\JWT\JWT::decode(): Argument #3 ($headers) could not be passed by reference in REDACTED.php:26
Stack trace:
#0 {main}
  thrown in REDACTED/test.php on line 26

[bshaffer]

Thanks a lot for catching and fixing this!