Incorrect URL in .download-urls
This was originally reported in passing here: #105 (comment 209050) and then reported against ghc here: ghc/ghc#16861 (closed); I didn't realise this is part of ghcup.
The binary distribution listed in https://gitlab.haskell.org/haskell/ghcup/blob/master/.download-urls for GHC 8.6.5 on centos links to a non-existent file: the link points to https://downloads.haskell.org/~ghc/8.6.5/ghc-x86_64-centos7-linux.tar.xz which does not exist.