MDL-76415 lib: Fixed ${var} str interpolation deprecations in php-jwt.

Since PHP 8.2, placing the dollar sign outside the curly brace is deprecated when
the expression inside the braces resolves to a variable or an expression.

lib/php-jwt/readme_moodle.txt

@@ -13,3 +13,9 @@ Instructions
 4.  Download the latest release.
 5.  Unzip it in lib as php-jwt.
 6.  Update entry for this library in lib/thirdpartylibs.xml.
+
+2023/01/26
+----------
+- src/JWT.php file has minor changes for PHP 8.2 compatibility. See MDL-76415 for more details.
+  Since version v6.3.1, the php-jwt already has the fix, so if someone executing the upgrading version and
+  it has the patch, please ignore this note.

lib/php-jwt/src/JWT.php

@@ -136,7 +136,7 @@ class JWT
             // OpenSSL expects an ASN.1 DER sequence for ES256/ES384 signatures
             $sig = self::signatureToDER($sig);
         }
-        if (!self::verify("${headb64}.${bodyb64}", $sig, $key->getKeyMaterial(), $header->alg)) {
+        if (!self::verify("{$headb64}.{$bodyb64}", $sig, $key->getKeyMaterial(), $header->alg)) { // TODO: Remove this modification in MDL-76415.
             throw new SignatureInvalidException('Signature verification failed');
         }