[Traffic Annotations] check_network_annotations when XML changes

Previously, if a CL only modified annotations.xml, CQ wouldn't run
check_network_annotations because the file doesn't appear in the
dependency tree for shipped_binaries.

This CL adds annotations.xml to shipped_binaries, solving that issue.

TESTED=Created a dependent CL that updates only annotations.xml and
       checked that it fails on CQ:
   https://chromium-review.googlesource.com/c/chromium/src/+/1758433

Change-Id: Ib33099df057f1cef882c46858862ea5fca5b91e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1757297
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Ramin Halavati <rhalavati@chromium.org>
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688482}

• BUILD.gn[diff]
• tools/traffic_annotation/summary/BUILD.gn[Added - diff]