doc/next: revert incorrect change to 62516.md made in CL 603959

Change-Id: I0d19f77f8c4b99350e3ed1e7f92db6ae198e812a
Reviewed-on: https://go-review.googlesource.com/c/go/+/607077


Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

doc/next/6-stdlib/99-minor/testing/62516.md

-The new [T.Context] and [B.Context] methods return a context that is canceled
-after the test completes and before test cleanup functions run.
+The new [T.Chdir] and [B.Chdir] methods can be used to change the working
+directory for the duration of a test or benchmark.