Revert "Meson: appinfo tests are racy if run in parallel"

This partially reverts commit 27b5fb5892.

The infrastructure for disabling a test is kept, but the appinfo and
desktop-app-info tests no longer need to be run serially.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://gitlab.gnome.org/GNOME/glib/issues/1601

gio/tests/meson.build

@@ -156,11 +156,9 @@ if host_machine.system() != 'windows'
     gio_tests += {
       'appinfo' : {
         'install' : false,
-        'is_parallel' : false,
       },
       'desktop-app-info' : {
         'install' : false,
-        'is_parallel' : false,
       },
     }
   endif