desktop: rustfmt the blob-store test

One hunk from run 2911. Clippy and all 67 tests — including the six new blob
tests and the path-traversal guard — had already passed on the same code.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SreJkbxB4gx8pPsu8QbLPi

desktop/src-tauri/src/sync/blobs.rs

@@ -135,7 +135,9 @@ mod tests {
     fn accepts_an_uppercase_hash() {
         // The wire format isn't guaranteed to be lowercase; the filename is.
         let store = store("case");
-        store.store(&HELLO.to_ascii_uppercase(), b"hello").expect("store");
+        store
+            .store(&HELLO.to_ascii_uppercase(), b"hello")
+            .expect("store");
         assert!(store.has(HELLO), "should be found under the lowercase name");
     }