Add OperatorLearning.jl to Flux downstream tests

This will be a more "Flux intensive" SciML repo than some of the others so I think it will be good to hear early and often about Flux changes there.

CC @pzimbrod

Author: ChrisRackauckas

.github/workflows/Downstream.yml

@@ -26,7 +26,7 @@ jobs:
           - {user: Chemellia, repo: AtomicGraphNets.jl, group: All}
           - {user: SciML, repo: DiffEqFlux.jl, group: Layers}
           - {user: SciML, repo: NeuralPDE.jl, group: NNPDE}
-
+          - {user: SciML, repo: OperatorLearning.jl, group: All}
     if: contains(github.event.pull_request.labels.*.name, 'run downstream test')
     steps:
       - uses: actions/checkout@v2