[Fuchsia] Add lsan to Fuchsia asan bot

The fuchsia asan runtime seems to include memory leak detection,
so build with is_asan=true

Bug: 1086888
Change-Id: I848e1b0b552a459488b08e7dbf91eefbbd142a2e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3384201


Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Chong Gu <chonggu@google.com>
Cr-Commit-Position: refs/heads/main@{#958424}