Run tests for MSRV, on macOS versions, and fix toolchain (#614)

* run tests on MSRV, for all macOS versions

* use dtolnay/rust-toolchain rather than unmaintained actions-rs/toolchain

* remove "msrv" build target as blocker for build result, as it is part of build

* update outdated actions/checkout

.github/workflows/rust.yml

@@ -24,27 +24,21 @@ jobs:
   semver:
     runs-on: macos-11.0
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Check semver
       uses: obi1kenobi/cargo-semver-checks-action@v2
-  msrv:
-    runs-on: macos-11.0
-    steps:
-    - uses: actions/checkout@v2
-    - name: Install toolchain
-      uses: actions-rs/toolchain@v1
-      with:
-        toolchain: 1.56.1
-        override: true
-    - name: Build
-      run: cargo build --verbose
   build:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os: [macos-11.0, macos-12, macos-13]
+        toolchain: [stable, 1.56.1]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
+    - name: Install toolchain
+      uses: dtolnay/rust-toolchain@master
+      with:
+        toolchain: ${{ matrix.toolchain }}
     - name: Build
       run: cargo build --verbose
     - name: Run tests
@@ -54,7 +48,6 @@ jobs:
     runs-on: ubuntu-latest
     needs:
       - "build"
-      - "msrv"
       - "semver"
     steps:
       - name: Mark the job as successful