pg_dump: tests: Correct test condition for invalid databases

For some reason I used not_like = { pg_dumpall_dbprivs => 1, } in the test
condition of one of the tests added in in c66a7d7. That doesn't make sense
for two reasons: 1) not_like isn't a valid test condition 2) the database
should not be dumped in any of the tests.  Due to 1), the test achieved its
goal, but clearly the formulation is confusing.  Instead use like => {}, with
a comment explaining why.

Reported-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/3ddf79f2-8b7b-a093-11d2-5c739bc64f86@eisentraut.org
Backpatch: 11-, like c66a7d7

src/bin/pg_dump/t/002_pg_dump.pl

@@ -1929,9 +1929,9 @@
 		    CREATE DATABASE regression_invalid;
 			UPDATE pg_database SET datconnlimit = -2 WHERE datname = 'regression_invalid'),
 		regexp => qr/^CREATE DATABASE regression_invalid/m,
-		not_like => {
-			pg_dumpall_dbprivs => 1,
-		},
+
+		# invalid databases should never be dumped
+		like => {},
 	},
 
 	'CREATE ACCESS METHOD gist2' => {