ci: add Downstream testset to CI

Author: AayushSabharwal

.github/workflows/ci.yml

@@ -12,7 +12,8 @@ jobs:
     strategy:
       matrix:
         group:
-          - All
+          - Core
+          - Downstream
         version:
           - '1'
     steps:
@@ -32,3 +33,5 @@ jobs:
             ${{ runner.os }}-
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
+        env:
+          GROUP: ${{ matrix.group }}