gitlab-backup/restore: Don't allow ln ambiguity (which can lead to failures)

ln has several syntaxes. man ln 1 ln:

   SYNOPSIS
          ln [OPTION]... [-T] TARGET LINK_NAME   (1st form)
          ln [OPTION]... TARGET                  (2nd form)
          ln [OPTION]... TARGET... DIRECTORY     (3rd form)
          ln [OPTION]... -t DIRECTORY TARGET...  (4th form)

so without -T or -t what is target and what is link name is ambiguous and
ln tries to guess. Now imagine:

    ln -sf /path/to/new/hook    $H

and let us consider that $H is already a symlink, pointing to some place
which _exists_, but current user do not have access to. Then ln will
complain:

    ln: accessing `$H': Permission denied

and abort.

Fix it by specifying ln form we use explicitly with -T.

contrib/gitlab-backup

@@ -284,7 +284,7 @@ backup_restore() {
     # adjust hooks links to point to current gitlab-shell location
     find "$reposX" -type l -path "*.git/hooks" | \
     while read H; do
-        ln -sf "$GITLAB_HOOKS_PATH" "$H"
+        ln -sfT "$GITLAB_HOOKS_PATH" "$H"
     done
 
     # extraction complete - now proceed with actual backup restore