Retry initial slurp_file("current_logfiles"), in test 004_logrotate.pl.

Buildfarm member topminnow failed when the test script attempted this
before the syslogger would have created the file.  Back-patch to v12,
which introduced the test.

src/bin/pg_ctl/t/004_logrotate.pl

@@ -21,7 +21,19 @@ $node->start();
 
 $node->psql('postgres', 'SELECT 1/0');
 
-my $current_logfiles = slurp_file($node->data_dir . '/current_logfiles');
+# might need to retry if logging collector process is slow...
+my $max_attempts = 180 * 10;
+
+my $current_logfiles;
+for (my $attempts = 0; $attempts < $max_attempts; $attempts++)
+{
+	eval {
+		$current_logfiles = slurp_file($node->data_dir . '/current_logfiles');
+	};
+	last unless $@;
+	usleep(100_000);
+}
+die $@ if $@;
 
 note "current_logfiles = $current_logfiles";
 
@@ -34,9 +46,6 @@ my $lfname = $current_logfiles;
 $lfname =~ s/^stderr //;
 chomp $lfname;
 
-# might need to retry if logging collector process is slow...
-my $max_attempts = 180 * 10;
-
 my $first_logfile;
 for (my $attempts = 0; $attempts < $max_attempts; $attempts++)
 {