fix: add missing cabal test tool dependency

+ hspec-discover should now be working in CI

Author: rasheedja

simplex-method.cabal

@@ -102,4 +102,6 @@ test-suite simplex-haskell-test
     , hspec >= 2.11.12 && < 2.12
     , hspec-expectations >= 0.8.3 && < 0.9
     , interpolatedstring-perl6 >= 1.0.2 && < 1.1
+  build-tool-depends:
+      hspec-discover:hspec-discover >= 2.11.12 && < 2.12
   default-language: Haskell2010