fix: Override disableSnapInstallation feature flag when using automatic updates (#3735)

Allow updates of Snaps even when the `disableSnapInstallation` feature
flag is enabled as long as the update is an automatic one.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Permits automatic Snap updates to bypass the `disableSnapInstallation`
check while preserving manual update restrictions for preinstalled
Snaps.
> 
> - **Snaps Controller** (`SnapController.ts`):
> - Modify `#updateSnap(...)` to only call `#assertCanInstallSnaps()`
when `automaticUpdate` is false, allowing automatic updates even if
`disableSnapInstallation` is enabled.
> - Retain restriction preventing manual updates of preinstalled Snaps
(`preinstalled && !automaticUpdate`).
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
4c35eb4. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: FrederikBolding

packages/snaps-controllers/src/snaps/SnapController.ts

@@ -2913,7 +2913,9 @@ export class SnapController extends BaseController<
     versionRange: SemVerRange;
     automaticUpdate?: boolean;
   }): Promise<TruncatedSnap> {
-    this.#assertCanInstallSnaps();
+    if (!automaticUpdate) {
+      this.#assertCanInstallSnaps();
+    }
     this.#assertCanUsePlatform();
 
     const snap = this.getExpect(snapId);