doc/go1.16: fix mismatched id attribute

For #40700.

Change-Id: I186a21899404bfb79c08bfa8623caf9da74b6b0d
GitHub-Last-Rev: 25d240d
GitHub-Pull-Request: #44145
Reviewed-on: https://go-review.googlesource.com/c/go/+/290329
Trust: Ian Lance Taylor <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: KimMachineGun

doc/go1.16.html

@@ -317,7 +317,7 @@ <h3 id="cgo">Cgo</h3>
 
 <h3 id="vet">Vet</h3>
 
-<h4 id="vet-string-int">New warning for invalid testing.T use in
+<h4 id="vet-testing-T">New warning for invalid testing.T use in
 goroutines</h4>
 
 <p><!-- CL 235677 -->