ci: split MTK downstream tests

Author: AayushSabharwal

.github/workflows/Downstream.yml

@@ -30,7 +30,10 @@ jobs:
           - {user: SciML, repo: SciMLSensitivity.jl, group: Core3}
           - {user: SciML, repo: SciMLSensitivity.jl, group: Core4}
           - {user: SciML, repo: SciMLSensitivity.jl, group: Core5}
-          - {user: SciML, repo: ModelingToolkit.jl, group: All}
+          - {user: SciML, repo: ModelingToolkit.jl, group: InterfaceI}
+          - {user: SciML, repo: ModelingToolkit.jl, group: InterfaceII}
+          - {user: SciML, repo: ModelingToolkit.jl, group: Initialization}
+          - {user: SciML, repo: ModelingToolkit.jl, group: SymbolicIndexingInterface}
           - {user: SciML, repo: DiffEqDevTools.jl, group: Core}
           - {user: nathanaelbosch, repo: ProbNumDiffEq.jl, group: Downstream}
           - {user: SKopecz, repo: PositiveIntegrators.jl, group: Downstream}