oauth2: minor perf-refactor when fetching a cluster (#41315)

Signed-off-by: Adi Suissa-Peleg <[email protected]>

Author: adisuissa

source/extensions/filters/http/oauth2/filter.cc

@@ -469,7 +469,7 @@ FilterConfig::FilterConfig(
            proto_config.cookie_configs().has_code_verifier_cookie_config())
               ? CookieSettings(proto_config.cookie_configs().code_verifier_cookie_config())
               : CookieSettings()) {
-  if (!context.clusterManager().clusters().hasCluster(oauth_token_endpoint_.cluster())) {
+  if (!context.clusterManager().hasCluster(oauth_token_endpoint_.cluster())) {
     // This is not necessarily a configuration error — sometimes cluster is sent later than the
     // listener in the xDS stream.
     ENVOY_LOG(warn, "OAuth2 filter: unknown cluster '{}' in config. ",