Allow meson builds to run test_pg_dump test in installcheck mode.

This had been disabled because the test "doesn't delete its user".
It doesn't seem like a great idea for the meson tests to act
differently from the makefile tests, though, and the makefiles
had no such exception (which is how come only copperhead noticed
the problem just fixed in 534287403).  In any case, the premise
is false since 936e3fa37, so let's remove the restriction.

Discussion: https://postgr.es/m/2857513.1713733688@sss.pgh.pa.us

src/test/modules/test_pg_dump/meson.build

@@ -13,8 +13,6 @@ tests += {
     'sql': [
       'test_pg_dump',
     ],
-    # doesn't delete its user
-    'runningcheck': false,
   },
   'tap': {
     'tests': [