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

The action dtolnay/rust-action does not exist.
The correct action is dtolnay/rust-toolchain.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: KaboomFox

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust
-        uses: dtolnay/rust-action@stable
+        uses: dtolnay/rust-toolchain@stable
 
       - name: Cache cargo
         uses: actions/cache@v4
@@ -41,7 +41,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust
-        uses: dtolnay/rust-action@stable
+        uses: dtolnay/rust-toolchain@stable
         with:
           components: rustfmt
 
@@ -55,7 +55,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust
-        uses: dtolnay/rust-action@stable
+        uses: dtolnay/rust-toolchain@stable
         with:
           components: clippy
 
@@ -80,7 +80,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust
-        uses: dtolnay/rust-action@stable
+        uses: dtolnay/rust-toolchain@stable
 
       - name: Check documentation
         run: cargo doc --no-deps --all-features
@@ -94,7 +94,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust 1.75
-        uses: dtolnay/rust-action@1.75
+        uses: dtolnay/rust-toolchain@1.75
 
       - name: Cache cargo
         uses: actions/cache@v4