widen CI tests to multiple platforms and julia versions

.github/workflows/ci.yml

@@ -15,9 +15,12 @@ jobs:
       fail-fast: false
       matrix:
         version:
-          - '1' # Leave this line unchanged. '1' will automatically expand to the latest stable 1.x release of Julia.
+          - '1.6'
+          - '1'
+          - 'nightly'
         os:
           - ubuntu-latest
+          - macOS-latest
         arch:
           - x64
     steps:
@@ -38,6 +41,7 @@ jobs:
             ${{ runner.os }}-
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
+        continue-on-error: ${{ matrix.version == 'nightly' }}
       - uses: julia-actions/julia-processcoverage@v1
       - uses: codecov/codecov-action@v3
         with: