Fix PHP 8.5 compatibility

* ord(): pass the first byte explicitly in encodeInteger(). PHP 8.5
  deprecates calling ord() with a string longer than one byte.
* CI: add PHP 8.5 to the phpunit matrix.

Author: shu-yusa

.github/workflows/ci.yml

@@ -14,6 +14,7 @@ jobs:
           - 8.2
           - 8.3
           - 8.4
+          - 8.5
     steps:
       - name: Checkout
         uses: actions/checkout@v4

src/SimpleJWT/Util/ASN1/DER.php

@@ -286,7 +286,7 @@ static function encodeInteger($int) {
         $data = gmp_export($int);
 
         if (strlen($data) == 0) return "\0";
-        if (ord($data) > 127) return "\0" . $data;
+        if (ord($data[0]) > 127) return "\0" . $data;
         return $data;
     }