Don't use --all flag with cargo fmt

This slows down the job considerably with no added benefit, see
rust-lang/rustfmt#4247 (comment)

Author: Mikhail Zabaluev

.github/workflows/test.yml

@@ -119,7 +119,7 @@ jobs:
         continue-on-error: false
         with:
           command: fmt
-          args: --all -- --check
+          args: -- --check
 
       - name: Restore cargo dependencies
         uses: actions/cache@v2