fix: Do not clear the schema cache during retries

retryingSchemaCacheLoad should not clear existing schema cache upon failure - there is no reason to do that. If there is a communication issue with the database server or db is down, clients are going to get 502 anyway. If it was a glitch when loading the schema cache - the clients are going to use old (stale) schema cache for some time until next retry re-loads it successfully.

src/PostgREST/AppState.hs

@@ -347,7 +347,6 @@ retryingSchemaCacheLoad appState@AppState{stateObserver=observer, stateMainThrea
       case result of
         Left e -> do
           markSchemaCachePending appState
-          putSchemaCache appState Nothing
           observer $ SchemaCacheErrorObs configDbSchemas configDbExtraSearchPath e
           return Nothing