A bunch of files have been missing from the tarballs created by `cabal
sdist`. I’ve changed the nix config to check for this and also found
some examples that I forgot to update in a previous PR (sorry about
that).
Note that even though we can now build grpc-haskell and grpc-haskell-core
with modern tasty, the environment in which we built those test programs
did not support actually running all them successfully, due to the need to test
generated code in the context of the appropriate libraries. We do not yet
know whether test programs built with new versions of tasty would succeed
in the appropriate environment. In principle this could be discovered, but
the work involved is far from trivial, and therefore we defer it to another
time. Tests built with the old tasty still succeed.
