ci: run Symbolics/Downstream in separate group until Core works

Author: AayushSabharwal

.github/workflows/Downstream.yml

@@ -23,6 +23,7 @@ jobs:
           - {user: SciML, repo: NeuralPDE.jl, group: NNPDE}
           - {user: SciML, repo: DataDrivenDiffEq.jl, group: Core}
           - {user: JuliaSymbolics, repo: Symbolics.jl, group: All}
+          - {user: JuliaSymbolics, repo: Symbolics.jl, group: Downstream}
           - {user: SciML, repo: ModelOrderReduction.jl, group: All}
 
     steps: