Give RecreateSKPs 8h

RecreateSKPs currently times out after 6h, but the "Build Chrome" step
is taking just shy of 6h by itself. As a result, the job is consistently
timing out shortly before finishing. Give the job an extra two hours to
complete.

Change-Id: I036b9562f530186de8188a778ae03e657023f400
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/938298
Reviewed-by: Eric Boren <borenet@google.com>