add ControlSystems to downstream (#494)

Author: jverzani

.github/workflows/downstream.yml

@@ -18,7 +18,7 @@ jobs:
         os: [ubuntu-latest]
         package:
           - {user: jverzani, repo: SpecialPolynomials.jl, group: All}
-          - {user: jverzani, repo: PolynomialsMutableArithmetics.jl, group: All}
+          - {user: JuliaControl, repo: ControlSystems.jl, group: All}
 
     steps:
       - uses: actions/checkout@v3