ci: test against MSRV

Author: weihanglo

.github/workflows/main.yml

@@ -7,23 +7,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        build: [stable, beta, nightly, macos, windows]
-        include:
-          - build: stable
-            os: ubuntu-latest
-            rust: stable
-          - build: beta
-            os: ubuntu-latest
-            rust: beta
-          - build: nightly
-            os: ubuntu-latest
-            rust: nightly
-          - build: macos
-            os: macos-latest
-            rust: stable
-          - build: windows
-            os: windows-latest
-            rust: stable
+        rust: ["1.66", stable, beta, nightly]
+        os: [ubuntu-latest, macos, windows]
     steps:
     - uses: actions/checkout@master
     - name: Install Rust (rustup)