Speedup CI: Always Use sparse registry

Signed-off-by: Jiahao XU <[email protected]>

Author: NobodyXu

.github/workflows/main.yml

@@ -1,6 +1,9 @@
 name: CI
 on: [push, pull_request]
 
+env:
+  CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
+
 jobs:
   test:
     name: Test