R1:28517110c6cb

Fix an issue in the new Harbormaster build log view where clicking the "^" icon doesn't work right

Summary:
Ref T13130. See PHI617.

The new build log UI has tags like `<a href="...">Show More Above <span icon>^</span></a>`. If you click the little "^" icon, the event target is the `<span />` instead of the `<a />` so we expand on the wrong node.

Instead, select the `<a />` by sigil explicitly.

Test Plan: Viewed new log UI in Harbormaster, clicked "^" icon and text, got the same (correct) behavior on…