config_types.Path will soon be replaced with pathlib.Path and
pathlib.Path doesn't have a join() method.
Bug: 329113288
Change-Id: I81bf607ffb41d84928af0eea06be78540b9912d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5467697
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Auto-Submit: Rob Mohr <mohrr@google.com>
Commit-Queue: Yiwei Zhang <yiwzhang@google.com>