Manually check out Rust toolchain in workflow

Author: lrettig

.github/workflows/ci.yml

@@ -51,7 +51,6 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: athenavm/athena
-          ref: rust-commit-hash
           path: athena
 
       - name: Get Rust commit
@@ -60,6 +59,18 @@ jobs:
           echo "Using Rust commit: $RUST_COMMIT"
           echo "RUST_COMMIT=$RUST_COMMIT" >> $GITHUB_ENV
 
+      # This is a shortcut to allow caching. If we don't manually check out Rust here,
+      # the Athena CLI tool will refuse to check it out since the cache will have
+      # already restored files into the same directory.
+      # This command won't check out submodules recursively. The cache restore will do
+      # this for us, saving time.
+      - name: Check out Rust toolchain
+        uses: actions/checkout@v4
+        with:
+          repository: rust-lang/rust
+          ref: ${{ env.RUST_COMMIT }}
+          path: toolchain/rust
+
       - uses: actions/cache@v4
         name: Cache Athena build
         with: