Only check MSRV/beta on ubuntu

Author: knutwalker

.github/workflows/checks.yml

@@ -95,8 +95,18 @@ jobs:
       fail-fast: false
       matrix:
         os: [windows-latest, macOS-latest, ubuntu-latest]
-        rust: [stable, beta, 1.63.0]
+        rust: [stable]
         flags: ['', --all-features]
+        include:
+          - os: ubuntu-latest
+            rust: {{ env.MSRV }}
+            flags: ''
+          - os: ubuntu-latest
+            rust: {{ env.MSRV }}
+            flags: '--all-features'
+          - os: ubuntu-latest
+            rust: beta
+            flags: '--all-features'
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout code