cros-workon: fix sandbox errors w/git worktrees

When using git worktrees, git might try to grab locks under the .repo
tree.  Add it to the predict list like we already do for the .git dir
in the source checkout.

BUG=None
TEST=CQ passes

Change-Id: Ida54a8f1cdc229e8f1b7c11f7376933e113077e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2065914
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/3998531
Reviewed-by: Stimim Chen <stimim@chromium.org>
Tested-by: Cheng Yueh <cyueh@chromium.org>
Commit-Queue: Stimim Chen <stimim@chromium.org>
1 file changed