Replace unmaintained actions-rs/toolchain action in CI workflows (#30)

Basically all of the `actions-rs/*` actions are unmaintained. See
<actions-rs/toolchain#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/ci.yml

@@ -14,11 +14,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: stable
           components: rustfmt, clippy
-          override: true
       - name: Cache Cargo build files
         uses: Leafwing-Studios/[email protected]
       - name: Install alsa and udev
@@ -31,10 +30,9 @@ 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 Cargo build files
         uses: Leafwing-Studios/[email protected]
       - name: Install alsa and udev
@@ -49,10 +47,9 @@ 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 Cargo build files
         uses: Leafwing-Studios/[email protected]
       - name: Install alsa and udev
@@ -65,7 +62,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: stable
       - name: Cache Cargo build files