inconsistent git clone behaviour

While creating https://github.com/JuliaPackaging/Yggdrasil/pull/4765 I noticed that in `run_wizard()`, the github repository was cloned into `${WORKSPACE}/srcdir/hptt.git`, but then when actually running `build_tarballs` this was `${WORKSPACE}/srcdir/hptt.git` so I had to modify the script.