builtin: clarify that interface types do not implement comparable
builtin: clarify that interface types do not implement comparable

Fixes #51083

Change-Id: Ic9207ae4104b06749925186e0eb4f18edf1b5007
Reviewed-on: https://go-review.googlesource.com/c/go/+/384235
Trust: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

nawawi/go,cloudflare/go,cloudflare/go,golang/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,nawawi/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,golang/go,CAFxX/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,golang/go,cloudflare/go,nawawi/go,golang/go,cloudflare/go