fix(test): Fix the "choose option to customize sync" Sync v1 test. (#5426) r=vladikoff
fix(test): Fix the "choose option to customize sync" Sync v1 test. (#5426) r=vladikoff

The original checkbox is not clickable after the amterial conversion.
The span next to the element holds the label text, click it instead.

fixes #5425
shane-tomlinson/fxa-content-server,shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,mozilla/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server