ci: add MTKNeuralNets to downstream CI

Author: AayushSabharwal

.github/workflows/Downstream.yml

@@ -37,6 +37,7 @@ jobs:
           - {user: SciML, repo: MethodOfLines.jl, group: Interface}
           - {user: SciML, repo: MethodOfLines.jl, group: 2D_Diffusion}
           - {user: SciML, repo: MethodOfLines.jl, group: DAE}
+          - {user: SciML, repo: ModelingToolkitNeuralNets.jl, group: All}
     steps:
       - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v1