fix(ci): attempt to specify the toolchain version explicitly in the Setup Rust github action, to avoid CI failures

Author: nickysn

.github/workflows/ci.yml

@@ -46,6 +46,8 @@ jobs:
           ruby-version: '3.2'
       - name: Setup Rust
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: stable
       - name: Install Ruby dependencies
         run: bundle install
       - name: Setup just