[perf] Fix bug in reading legacy Alert values.
[perf] Fix bug in reading legacy Alert values.

alert.NewConfig set the String values for the new parameters, which
made upgradeAlert a no-op.

Bug: skia:10489
Change-Id: I466c6d211f10a938142c9a122d310de1678beda0
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/301816
Reviewed-by: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Commit-Queue: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@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