Fix the 006_transfer_modes.pl test.

This test was leaving files like delete_old_cluster.sh in the
source directory for VPATH and meson builds.  To fix, change the
directory to tmp_check before running the test, as was done in
commits 15b6d21, 8af917b, and c462b05.

Oversight in commit af0d490.

Reported-by: Andrew Dunstan <andrew@dunslane.net> (on Discord)
Discussion: ???

Author: nathan-bossart

src/bin/pg_upgrade/t/006_transfer_modes.pl

@@ -102,6 +102,11 @@ sub test_mode
 	$new->clean_node();
 }
 
+# In a VPATH build, we'll be started in the source directory, but we want
+# to run pg_upgrade in the build directory so that any files generated finish
+# in it, like delete_old_cluster.{sh,bat}.
+chdir ${PostgreSQL::Test::Utils::tmp_check};
+
 test_mode('--clone');
 test_mode('--copy');
 test_mode('--copy-file-range');