Fix to use a tab instead of spaces (#8394)

## Problem
There were spaces instead of a tab in the C source file.

## Summary of changes
I fixed to use a tab instead of spaces.

pgxn/neon/neon.c

@@ -597,7 +597,7 @@ _PG_init(void)
 
 	pg_init_libpagestore();
 	pg_init_walproposer();
-        WalSender_Custom_XLogReaderRoutines = NeonOnDemandXLogReaderRoutines;
+	WalSender_Custom_XLogReaderRoutines = NeonOnDemandXLogReaderRoutines;
 	LogicalFuncs_Custom_XLogReaderRoutines = NeonOnDemandXLogReaderRoutines;
 
 	InitLogicalReplicationMonitor();