With sphinx 4, interpreting the conf.py fails due to a decode
error: https://gitlab.haskell.org/ghc/ghc/-/issues/19962
The fix is an one line change which we have to backport from GHC master.
Thus ghcHEAD is not affected by this problem.
9.2 and 8.10.6 will most likely have a fix for this.
TODO: Patch 8.8.4 and 9.0.1
