meson: Set install_tag on installed tests files

This could be done automatically by Meson, this commit can be reverted
when we have that Meson PR in our CI:
https://github.com/mesonbuild/meson/pull/10829

gio/tests/services/meson.build

@@ -25,6 +25,7 @@ foreach service_file : dbus_service_files
     )
     install_data(meson.current_build_dir() / service_file + '.to-install',
       install_dir: installed_tests_execdir / 'services',
+      install_tag: 'tests',
       rename: [service_file],
     )
   endif