debian9 nightly build failing due to older sphinx version
See https://gitlab.haskell.org/ghc/ghc/-/jobs/1639202
===> Command failed with error code: 1
Extension error:
Could not import extension flags (exception: No module named 'packaging')
Running Sphinx v1.4.9
haddock: user interrupt
Error when running Shake build system:
at want, called at src/Main.hs:124:44 in main:Main
* Depends on: binary-dist
at apply1, called at src/Development/Shake/Internal/Rules/Rerun.hs:41:5 in shake-0.19.7-210fc1cbce69aed26102707e3a1f9a8d35afdb700b5ceb2aa5cba89db1cc9fcb:Development.Shake.Internal.Rules.Rerun
* Depends on: binary-dist-dir
at need, called at src/Rules/BinaryDist.hs:220:24 in main:Rules.BinaryDist
* Depends on: docs
at need, called at src/Rules/Documentation.hs:129:9 in main:Rules.Documentation
* Depends on: _build/doc/users_guide.pdf
at cmd', called at src/Builder.hs:393:23 in main:Builder
at cmdArgs, called at src/Builder.hs:573:8 in main:Builder
at cmdArgs, called at src/Builder.hs:597:18 in main:Builder
at cmdArgs, called at src/Builder.hs:597:18 in main:Builder
at error, called at src/Builder.hs:642:13 in main:Builder
* Raised the exception:
Command failed
Build failed.