Update and simplify GH action scripts

Author: LukasKalbertodt

.github/workflows/ci.yml

@@ -12,43 +12,17 @@ env:
 jobs:
   style:
     name: 'Check basic style'
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v6
     - name: Check basic style
       run: ./.github/check-basic-style.sh
 
   check:
     name: 'Build & test'
-    runs-on: ubuntu-20.04
-    strategy:
-      matrix:
-        rust:
-          - stable
-          - beta
-          - nightly
+    runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
-    - name: Install Rust toolchain
-      uses: actions-rs/toolchain@v1
-      with:
-        toolchain: ${{ matrix.rust }}
-        override: true
-        profile: minimal
-    - name: Prepare cache key
-      run: |
-        cargo generate-lockfile
-        cp Cargo.lock cache-fingerprint
-        echo $RUSTFLAGS >> cache-fingerprint
-        echo $(rustc -V) >> cache-fingerprint
-    - name: Restore cargo cache
-      uses: actions/cache@v2
-      with:
-        path: |
-          ~/.cargo/registry
-          ~/.cargo/git
-          target
-        key: ${{ runner.os }}-cargo-${{ hashFiles('cache-fingerprint') }}
+    - uses: actions/checkout@v6
     - name: Build
       run: cargo build
     - name: Build benchmarks
@@ -59,12 +33,11 @@ jobs:
     - name: Generate docs
       run: cargo doc
 
-  # We do not use a cache here as Miri prefers a clean working directory anyway.
   check-miri:
     name: 'Run tests with miri'
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v6
     - name: Install Rust toolchain
       uses: actions-rs/toolchain@v1
       with: