tests/kvm: Bump timeout to 60 s

It can be quite slow to set up the test environment inside the VM, as
well as outside, leaving very little time for the test itself. While
it'd be nice to not run the mock env etc outside the VM, let's just bump
the timeout for now, to avoid unnecessary timeout failures.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2777>

src/tests/kvm/meson.build

@@ -57,5 +57,6 @@ foreach test_case: privileged_tests
       test_case['executable'].full_path(),
     ],
     is_parallel: false,
+    timeout: 60,
   )
 endforeach