go/types: simplify use of TestManual
go/types: simplify use of TestManual

This is a 1:1 port of CL 315689 to go/types.

Change-Id: If71186b3719be8433c9d21b22c51ffde2cadd55b
Reviewed-on: https://go-review.googlesource.com/c/go/+/315849
Trust: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
Run-TryBot: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

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