Add 'static' to file-local variables missing it.

Noticed when comparing the set of exported symbols without / with
-fvisibility=hidden after adding PGDLLIMPORT to intentionally exported
symbols.

Discussion: https://postgr.es/m/20220512164513.vaheofqp2q24l65r@alap3.anarazel.de

src/backend/replication/logical/launcher.c

@@ -65,7 +65,7 @@ typedef struct LogicalRepCtxStruct
 	LogicalRepWorker workers[FLEXIBLE_ARRAY_MEMBER];
 } LogicalRepCtxStruct;
 
-LogicalRepCtxStruct *LogicalRepCtx;
+static LogicalRepCtxStruct *LogicalRepCtx;
 
 static void ApplyLauncherWakeup(void);
 static void logicalrep_launcher_onexit(int code, Datum arg);

src/backend/replication/logical/tablesync.c

@@ -124,7 +124,7 @@ static bool table_states_valid = false;
 static List *table_states_not_ready = NIL;
 static bool FetchTableStates(bool *started_tx);
 
-StringInfo	copybuf = NULL;
+static StringInfo copybuf = NULL;
 
 /*
  * Exit routine for synchronization worker.

src/backend/replication/logical/worker.c

@@ -251,7 +251,7 @@ static MemoryContext LogicalStreamingContext = NULL;
 WalReceiverConn *LogRepWorkerWalRcvConn = NULL;
 
 Subscription *MySubscription = NULL;
-bool		MySubscriptionValid = false;
+static bool MySubscriptionValid = false;
 
 bool		in_remote_transaction = false;
 static XLogRecPtr remote_final_lsn = InvalidXLogRecPtr;