doc/go1.20: correct test binary -v flag value for test2json
The -v flag value is "test2json", not "json", since it emits output
in a custom format that the cmd/test2json tool interprets.
The cmd/test2json documentation and implementation have this right.
For #54202.
Change-Id: I2b52861d926e14488aa9fc89fff8c26da32ca710
Reviewed-on: https://go-review.googlesource.com/c/go/+/456124 Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>