[hadrian] stack.yaml out of sync with hadrian.cabal

Summary

Hadrian stack.yaml out of sync with it's hadrian.cabal.

I see that the Cabal file for Hadrian now requires happy-1.20.0 but the stack resolver lts-16.14 gives 1.19.12.

A possible resolution is to update hadrian/stack.yaml so:

extra-deps:
 - happy-1.20.0

I found this testing builds of ghc-lib against HEAD. I'm guessing that we don't have any stack/hadrian configs in CI.

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