pin once_cell

Author: kylebarron

.github/workflows/ci.yml

@@ -118,6 +118,7 @@ jobs:
         name: Set MSRV dependencies
         run: |
           cargo add tokio@=1.38.1
+          cargo update -p once_cell --precise 1.20.3
 
       - name: Build (no features)
         run: cargo build --no-default-features --verbose --target ${{ matrix.platform.rust-target }}