tests: Mark two more tests as slow

These keep on taking just longer than 30s on my local machine when run
in parallel with the rest of the tests (i.e. with `ninja test`). Testing
them individually, they do terminate correctly.

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

tests/refcount/meson.build

@@ -1,5 +1,5 @@
 refcount_tests = [
- ['closures', 'closures.c', []],
+ ['closures', 'closures.c', [], 90],
  ['objects', 'objects.c', []],
  ['objects2', 'objects2.c', [], 90],
  ['properties', 'properties.c', []],