update: wrap the dev-rolling feed assertion the way rustfmt wants

7296889 lengthened `/dev/latest.json` to `/dev-rolling/latest.json` in
each_channel_has_its_own_fixed_feed, which pushed the assert past the
line width. `cargo fmt --all --check` failed the Linux desktop job (run
6358) after Clippy and the tests had passed, so that build, its publish
and the manifest job never ran. Layout taken verbatim from the diff
rustfmt printed; no behaviour change.

Scribe #2184.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DwoKYuw3qJmUUYsJeNherB

desktop/src-tauri/src/update.rs

@@ -444,7 +444,9 @@ mod tests {
     #[test]
     fn each_channel_has_its_own_fixed_feed() {
         assert!(Channel::Stable.feed_url().ends_with("/stable/latest.json"));
-        assert!(Channel::Dev.feed_url().ends_with("/dev-rolling/latest.json"));
+        assert!(Channel::Dev
+            .feed_url()
+            .ends_with("/dev-rolling/latest.json"));
         assert_ne!(Channel::Stable.feed_url(), Channel::Dev.feed_url());
     }