Custom features repo branch in CI until after 1.3.0 (#338)

Author: cretz

.github/workflows/ci.yml

@@ -134,3 +134,4 @@ jobs:
       dotnet-repo-path: ${{github.event.pull_request.head.repo.full_name}}
       version: ${{github.event.pull_request.head.ref}}
       version-is-repo-ref: true
+      features-repo-ref: "dotnet-after-1.3.0"