Fix CI: use dtolnay/rust-toolchain instead of rust-action

The action dtolnay/rust-action doesn't exist. The correct action
is dtolnay/rust-toolchain.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: noahgift

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust
-        uses: dtolnay/rust-action@stable
+        uses: dtolnay/rust-toolchain@stable
         with:
           components: clippy, rustfmt
 
@@ -48,7 +48,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust
-        uses: dtolnay/rust-action@stable
+        uses: dtolnay/rust-toolchain@stable
         with:
           targets: wasm32-unknown-unknown
 
@@ -64,7 +64,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust
-        uses: dtolnay/rust-action@stable
+        uses: dtolnay/rust-toolchain@stable
 
       - name: Run benchmarks
         run: cargo bench -p presentar-core --no-run