If there is a warning during validate_step_info and the step_info is
None, the script should not attempt to update that step in the
Spreadsheet object.

Bug: angleproject:4030
Change-Id: Ib94ba82219745ee4ab36c52e9b1d3a04a76a05d2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1872569Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>