Refer to python3 in asan_symbolize.py script.

Change-Id: I6b4acfba41514a9d6981d9e4721495c0ff480f89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5830775
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Adrian Taylor <adetaylor@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1417314}
NOKEYCHECK=True
GitOrigin-RevId: 82b06206cd06119cc627400fcb1706fc49fb83b1