Replace unmaintained actions-rs/toolchain action in CI workflows

Basically all of the `actions-rs/*` actions are unmaintained. See
<https://github.com/actions-rs/toolchain/issues/216> for more
information. Due to their age they generate several warnings in
CI runs.

To get rid of those warnings the occurrences of
`actions-rs/toolchain` are replaced by `dtolnay/rust-toolchain`.

.github/workflows/book.yml

@@ -10,10 +10,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: stable
-          override: true
 
       - name: Cache dependencies
         uses: actions/cache@v3

.github/workflows/release.yml

@@ -39,11 +39,10 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}
-          override: true
-          target: wasm32-unknown-unknown
+          targets: wasm32-unknown-unknown
 
       - name: Query version number
         id: get_version

.github/workflows/test.yml

@@ -30,11 +30,10 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: nanasess/setup-chromedriver@master
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}
-          override: true
-          target: wasm32-unknown-unknown
+          targets: wasm32-unknown-unknown
       - uses: actions/setup-node@v2
 
       - name: Cache dependencies