test against SingularIntegralEquations.jl (#177)

Author: jishnub

.github/workflows/downstream.yml

@@ -23,6 +23,7 @@ jobs:
           - {repo: ApproxFunOrthogonalPolynomials.jl, group: JuliaApproximation}
           - {repo: ApproxFunFourier.jl, group: JuliaApproximation}
           - {repo: ApproxFunSingularities.jl, group: JuliaApproximation}
+          - {repo: SingularIntegralEquations.jl, group: JuliaApproximation}
 
     steps:
       - uses: actions/checkout@v2