fix: Do not emit :registryUpdated on failure (#3949)

BugBot indicated that my previous PR had a infinite loop in case of the
registry failure state:
#3948 (comment)

We do not need to emit `:registryUpdated` on failure, which should fix
this problem.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: a small behavioral change to event emission that only
affects failure paths, reducing the chance of update-trigger loops when
the registry is unavailable.
> 
> **Overview**
> Prevents `SnapRegistryController` from publishing the
`SnapRegistryController:registryUpdated` event when `#update()` fails
(e.g., fetch/verify errors), while still marking `databaseUnavailable`
in state.
> 
> Successful updates and no-op updates (recent fetch or unchanged
signature) continue to emit `:registryUpdated` as before.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
8af7c86. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: FrederikBolding

packages/snaps-controllers/src/snaps/registry/SnapRegistryController.ts

@@ -262,7 +262,6 @@ export class SnapRegistryController extends BaseController<
       this.update((state) => {
         state.databaseUnavailable = true;
       });
-      this.messenger.publish('SnapRegistryController:registryUpdated', false);
     }
   }