fix: adjust expiration time for token generation

GitHub recently tightened JWT validation for GitHub App authentication as the `exp` claim must now be strictly less than 10 minutes from `iat`

Author: docimin

src/VCS/Adapter/Git/GitHub.php

@@ -600,7 +600,7 @@ protected function generateAccessToken(string $privateKey, ?string $appId): void
         $appIdentifier = $appId;
 
         $iat = time();
-        $exp = $iat + 10 * 60;
+        $exp = $iat + 9 * 60;
         $payload = [
             'iat' => $iat,
             'exp' => $exp,