[cq_watcher] Make dummy alert labels match real alert labels
[cq_watcher] Make dummy alert labels match real alert labels

Without this cq_watcher crashes with:
"""
Failed to register "cq_watcher_in_flight_trybot_duration": a previously
registered descriptor with the same fully-qualified name as Desc{fqName:
"cq_watcher_in_flight_trybot_duration", help:
"cq_watcher_in_flight_trybot_duration", constLabels: {}, variableLabels:
[gerritURL trybot]} has different label names or a different help
string
"""

Bug: skia:10007
Change-Id: I758fe9baff6c00b3214155c1204ce6d569bf735b
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/275317
Reviewed-by: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot