internal/trace/v2: fix reader version for dumping text output
There was recently a failure that we don't have a trace dump for because
the reader was passed Go122 but traces have moved onto version Go123.
Use version.Current to prevent this from happening again in the future.
Change-Id: I4f8b3c3ea5bad61a07839a697cd5d7793d62ea52
Reviewed-on: https://go-review.googlesource.com/c/go/+/574216
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Carlos Amedee <carlos@golang.org>