Add "manual" to mozc_objc_test.macos_unit_test.

* Suppress the CI error on GitHub Actions.
* To address the root cause we probably need to update the upstream of google-toolbox-for-mac.
  + google/google-toolbox-for-mac#407

#codehealth

PiperOrigin-RevId: 531506258

src/build_defs.bzl

@@ -255,7 +255,7 @@ def mozc_objc_test(
         size = size,
         visibility = visibility,
         target_compatible_with = ["@platforms//os:macos"],
-        tags = MOZC_TAGS.MAC_ONLY + tags,
+        tags = ["manual"] + MOZC_TAGS.MAC_ONLY + tags,
     )
 
 register_extension_info(