Second attempt to fix pgbench TAP test.

Bildfarm member prairiedog reported a pgbench TAP test failure after
commit: 4a39f87acd. This is the second
attempt to fix it. It seems older version of Perl does not accept
"\gN". Replace it with plain old "\N" because actually "\gN" is not
necessary here.

Author: Tatsuo Ishii
Reported-by: Tom Lane
Reviewed-by: Tom Lane, Yugo Nagata
Discussion: https://postgr.es/m/2775989.1648060014%40sss.pgh.pa.us

src/bin/pgbench/t/001_pgbench_with_server.pl

@@ -1222,9 +1222,9 @@ local $ENV{PGOPTIONS} = "-c default_transaction_isolation=repeatable\\ read";
 # delta variable in the next try
 my $err_pattern =
 	"(client (0|1) sending UPDATE xy SET y = y \\+ -?\\d+\\b).*"
-  . "client \\g2 got an error in command 3 \\(SQL\\) of script 0; "
+  . "client \\2 got an error in command 3 \\(SQL\\) of script 0; "
   . "ERROR:  could not serialize access due to concurrent update\\b.*"
-  . "\\g1";
+  . "\\1";
 
 $node->pgbench(
 	"-n -c 2 -t 1 -d --verbose-errors --max-tries 2",