Gerrit allows multiline footers with indents.
e.g.,
Test: something
looks great
This CL fixes the bug such that add_footer correctly inserts
a given message after multiline footers.
Bug: 379923433
Change-Id: I9b3f793095b63b0586123543a2f8d49f0503fca0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6064963
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Scott Lee <ddoman@chromium.org>