git-checkout: Invoke git fetch with --unshallow

Melange currently barfs on specific cherry-pick situations like the
one at wolfi-dev/os#74858 .  I spent some time
investigating this and found that this happens because the initial
`git clone` to fetch a tag is done in shallow mode, and then
subsequent `git fetch` commands will be constrained by the
"shallowness" that was created.  I was surprised to find @smoser's
#1473 which pretty
much reached the same conclusion.

My suggestion is that we should bite the bullet here and just invoke
the `git fetch` that's run during `cherry-pick` using the
`--unshallow` option.  The downside is that this will pull in the
entire repository history, which can be a lot in some cases.

Signed-off-by: Sergio Durigan Junior <sergiodj@chainguard.dev>

Author: sergiodj

pkg/build/pipelines/git-checkout.yaml

@@ -121,7 +121,7 @@ pipeline:
             if [ -n "$branch" ]; then
                 case " $fetched_branches " in
                     *" $branch "*) ;;
-                    *) vr git fetch origin $branch:$branch || {
+                    *) vr git fetch --unshallow origin $branch:$branch || {
                         msg "failed to fetch branch $branch"
                         return 1
                         }