[firestore] Less error spew on exit
[firestore] Less error spew on exit

We stopped actually retrying for "context canceled" in
https://skia-review.googlesource.com/c/buildbot/+/248930 but we're still
logging errors. This should prevent spurious "error rate" alerts after
pushes.

Change-Id: I10a15be234a53596c5f379047a71762f33cbd30d
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/253176
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Reviewed-by: Ben Wagner aka dogben <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Reviewed-by: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@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