Hadrian skips Haddock tests by default

In the CI pipeline https://gitlab.haskell.org/ghc/ghc/pipelines/14835 Hadrian jobs pass but make jobs fail. Why? The patch introduces a bug that breaks the haddockHypsrcTest test, but the Hadrian jobs do not run this test.

The test suite skips Haddock tests due to missing libraries. To reproduce locally, run hadrian/build.sh -j --flavour=Quick test --only="haddockHypsrcTest" on a fresh clone of GHC. You will see the following message after the test driver runs:

1 had missing libraries, 0 expected passes

Then, if you run hadrian/build.sh -j --flavour=Quick docs-haddock, it will build the required library, and this time running the haddockHypsrcTest test will report:

0 had missing libraries, 1 expected passes

We must make sure that this is what happens on CI, or we won't catch similar issues if we get rid of make jobs as suggested in #17527 (closed)