fix: do not throw UpdateException on SHOREBIRD_NO_UPDATE (#334)

`ShorebirdUpdater.update()` previously threw `UpdateException: No update
(noUpdate)` whenever the patch check returned no available update, even
though that is a successful outcome of calling `update()` — the app is
already running the latest patch.

The wrapper only returned normally on `SHOREBIRD_UPDATE_INSTALLED`;
every other status (including `SHOREBIRD_NO_UPDATE`, value 0) fell
through to the generic `throw UpdateException(...)` path, which is
why callers saw `UpdateException: No update (noUpdate)` in their
exception telemetry.

Treat `SHOREBIRD_NO_UPDATE` as a successful return alongside
`SHOREBIRD_UPDATE_INSTALLED`. No FFI change, safe against any engine
version (status code 0 is stable).

Fixes shorebirdtech/shorebird#3681

shorebird_code_push/lib/src/shorebird_updater_io.dart

@@ -117,7 +117,14 @@ class ShorebirdUpdaterImpl implements ShorebirdUpdater {
 
       final status = result.ref.status;
 
-      if (status == SHOREBIRD_UPDATE_INSTALLED) return;
+      // SHOREBIRD_UPDATE_INSTALLED is the success case. SHOREBIRD_NO_UPDATE
+      // (the app is already up to date) is also a successful outcome of a call
+      // to update() and must not throw — previously it surfaced as a confusing
+      // `UpdateException: No update (noUpdate)` in customer telemetry.
+      if (status == SHOREBIRD_UPDATE_INSTALLED ||
+          status == SHOREBIRD_NO_UPDATE) {
+        return;
+      }
 
       final reason = status.toFailureReason();
       final message = result.ref.message != nullptr