docs: Add comments to action.yml regarding changing the rust version

.github/actions/setup-env/action.yml

@@ -7,6 +7,12 @@ runs:
     - name: Install Rust toolchain
       uses: RDXWorks-actions/toolchain@master
       with:
+        # IMPORTANT: If you update this Rust version:
+        # * Ensure you also update it in the README in two places:
+        #   - "Install Rust - we recommend to use Rust XXXX"
+        #   - "rustup default XXXX"
+        # * Ensure you update the version in the "radix-clis-scrypto-coverage" step,
+        #   or update the comment explaining why a different version is used.
         toolchain: 1.80.1
         default: true
         target: wasm32-unknown-unknown

.github/workflows/ci.yml

@@ -316,6 +316,8 @@ jobs:
           shared-key: radix-clis-debug-${{ runner.os }}
           cache-directories: ~/.cargo/registry/src/**/librocksdb-sys-*
           workspaces: radix-clis
+      # Coverage needs a nightly compiler.
+      # This should be at or in front of the default toolchain defined in action.yml
       - name: Install rustc 1.81.0-nightly
         run: |
           rustup toolchain install nightly-2024-07-18