testing: silly typo in documentation

[seebs]

What version of Go are you using (go version)?

$ go version
1.19.2

Does this issue reproduce with the latest release?

y

What operating system and processor architecture are you using (go env)?

N/A

What did you do?

Read the docs.

What did you expect to see?

Fewer typos.

What did you see instead?

In the FuzzJSONMarshaling example:

t.Error("Marshal: %v", err)

Either this shouldn't have the "%v", or it should be t.Errorf.

[ianlancetaylor]

Thanks, sending a CL.

[gopherbot]

Change https://go.dev/cl/446275 mentions this issue: testing: change Error to Errorf in comment