pkg/git: fix ssh credentials detection 🦀
pkg/git: fix ssh credentials detection 🦀

To detect ssh cerdentials (and validate the git clone url with
cerdentials), we do check if there is a `$HOME/.ssh` folder. With
`disable-home-env-overwrite` we do not overwrite `$HOME` env anymore,
and thus we have *no* control where `$HOME` is and wether the image
ships it with a `.ssh` or not.

This fixes it by looking at a path we control no matter how the
controller is configured : `pipeline.CredsDir` (`/tekton/creds`).

Signed-off-by: Vincent Demeester <b98c0fd48a8945096c766de790fe70420dd2f223@redhat.com>

tektoncd/pipeline,tektoncd/pipeline