testing: treat PAUSE lines as changing the active test name
We could instead fix cmd/test2json to treat PAUSE lines as *not*
changing the active test name, but that seems like it would be more
confusing to humans, and also wouldn't fix tools that parse output
using existing builds of cmd/test2json.
Fixes #40657
Change-Id: I937611778f5b1e7dd1d6e9f44424d7e725a589ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/248727
Run-TryBot: Bryan C. Mills <bcmills@google.com> Reviewed-by: Jean de Klerk <deklerk@google.com>