doc/go1.17: document testing changes for Go 1.17

For #44513. Fixes #46024

Change-Id: Icf3877d1fcd67448fbc79a0ce3db3f319ad4a0e9
GitHub-Last-Rev: 8c01593
GitHub-Pull-Request: #46324
Reviewed-on: https://go-review.googlesource.com/c/go/+/322109
Reviewed-by: Heschi Kreinick <heschi@google.com>
Trust: Jeremy Faller <jeremy@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>

doc/go1.17.html

@@ -659,9 +659,8 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 <dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
  <dd>
  <p><!-- CL 310033 -->
- TODO: <a href="https://golang.org/cl/310033">https://golang.org/cl/310033</a>: add -shuffle=off|on|N to alter the execution order of tests and benchmarks
+ Added a new <a href="/cmd/go/#hdr-Testing_flags">testing flag</a> <code>-shuffle</code> which controls the execution order of tests and benchmarks.
  </p>
-
  <p><!-- CL 260577 -->
  The new
  <a href="/pkg/testing/#T.Setenv"><code>T.Setenv</code></a>