fix(test): mock load method for hashtag preferences service

- Adds `load: async () => {}` to the `hashtagPreferences` mock in `tests/profile-modal-controller.test.mjs`.
- Fixes `TypeError: this.hashtagPreferencesService.load is not a function` during `handleAddHashtagPreference` test execution.

Co-authored-by: PR0M3TH3AN <[email protected]>

tests/profile-modal-controller.test.mjs

@@ -274,6 +274,7 @@ function createController(options = {}) {
       return hashtagStore.disinterests.delete(normalized);
     },
     publish: async () => ({ ok: true }),
+    load: async () => {},
     on: () => () => {},
   };