postgres_fdw: Fix test failure with -DENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
The roles created by regression test should have names starting with
"regress_", and the test introduced in commit
411ae64997 did not do that.
Per buildfarm member longfin.
Discussion: https://postgr.es/m/
73fc5ae4-3c54-1262-4533-
f8c547de2e60@oss.nttdata.com