Add test 005_char_signedness.pl to meson.build.

Oversight in a8238f8 where the test has been added.

Discussion: https://postgr.es/m/CB11ADBC-0C3F-4FE0-A678-666EE80CBB07%40amazon.com

Author: MasahikoSawada

src/bin/pg_upgrade/meson.build

@@ -45,6 +45,7 @@ tests += {
       't/002_pg_upgrade.pl',
       't/003_logical_slots.pl',
       't/004_subscription.pl',
+      't/005_char_signedness.pl',
     ],
     'test_kwargs': {'priority': 40}, # pg_upgrade tests are slow
   },