hadrian: exclude cabal.project.symlink.broken from source archives

Cabal 3.14 introduced a broken symlink in its testsuite. Unfortunately,
this broke our source distribution as we use use `tar --dereference` to avoid
issues with symlink compatibility on windows, and `tar --dereference` chokes
when it encounters any broken symlinks.

We can't get rid of `--dereference` because symlinks are generally broken on
windows, so the only option is to exclude this file from source archives.

see also https://github.com/haskell/cabal/issues/10442

(cherry picked from commit 16f97667)