ci: remove explicit formatting of the benchmarks

Running `cargo fmt` in the folder above already covers the benchmarks.

Author: LingMan

.github/workflows/ci.yml

@@ -95,10 +95,6 @@ jobs:
     - name: Check formatting
       run: |
         cargo fmt -- --check
-    - name: Check formatting in ./bench
-      working-directory: ./bench
-      run: |
-        cargo fmt -- --check
 
   miri:
     name: miri