chore: fix latest php-cs-fixer findings

Author: sbuerk

src/CachedKeySet.php

@@ -180,7 +180,7 @@ private function keyIdExists(string $keyId): bool
             $jwksResponse = $this->httpClient->sendRequest($request);
             if ($jwksResponse->getStatusCode() !== 200) {
                 throw new UnexpectedValueException(
-                    sprintf('HTTP Error: %d %s for URI "%s"',
+                    \sprintf('HTTP Error: %d %s for URI "%s"',
                         $jwksResponse->getStatusCode(),
                         $jwksResponse->getReasonPhrase(),
                         $this->jwksUri,

src/JWK.php

@@ -212,7 +212,7 @@ private static function createPemFromCrvAndXYCoordinates(string $crv, string $x,
                 )
             );
 
-        return sprintf(
+        return \sprintf(
             "-----BEGIN PUBLIC KEY-----\n%s\n-----END PUBLIC KEY-----\n",
             wordwrap(base64_encode($pem), 64, "\n", true)
         );