One can end up in detached head upon checking out a tag already. Thus
move config to remove detached head warning earlier, before any git
commands are executed.

Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@chainguard.dev>

Initialize a bare repository in melange cache and fetch all potential
desired objects into it.

Then continue git clone as before.

This means that any package rebuilds will be quicker
w.r.t. git-checkout pipeline action.

Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@chainguard.dev>