chore(ci): pin tokio-util in MSRV CI job (#149)

Author: seanmonstar

.github/workflows/CI.yml

@@ -68,10 +68,11 @@ jobs:
         uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}
-      - name: Make sure tokio 1.38.1 is used for MSRV
+      - name: Pin some dependencies for MSRV
         run: |
           cargo update
           cargo update --package tokio --precise 1.38.1
+          cargo update --package tokio-util --precise 0.7.11
       - run: cargo check --features full
 
   miri: