Update ci.yml

Author: ChrisRackauckas

.github/workflows/ci.yml

@@ -15,6 +15,10 @@ jobs:
           - Core
         version:
           - '1'
+        os:
+          - ubuntu-latest
+          - macos-latest
+          - windows-latest
     steps:
       - uses: actions/checkout@v5
       - uses: julia-actions/setup-julia@v1
@@ -37,4 +41,4 @@ jobs:
       - uses: julia-actions/julia-processcoverage@v1
       - uses: codecov/codecov-action@v5
         with:
-          file: lcov.info
+          file: lcov.info