ci: Pass -Werror when building hadrian in hadrian-ghc-in-ghci job

Warnings when building Hadrian can end up cluttering the output of HLS, and we've had bug reports in the past about these warnings when building Hadrian. It would be nice to turn on -Werror on at least one build of Hadrian in CI to avoid a patch introducing warnings when building Hadrian.

Fixes #23638 (closed)