cmd/go/internal/modload: ignore disallowed errors when checking for updates

cmd/go/internal/modload: ignore disallowed errors when checking for updates

addUpdate calls Query with the query "upgrade". Normally, this returns
the highest release version (or prerelease, etc.) that is higher than
the current version and is not retracted or excluded. If there is no
such version, Query should return the current version. If the current
version is retracted or excluded, then Query currently returns an error.

addUpdate should ignore this error, as it ignores ErrNotExist and
NoMatchingVersionError. For 'go list -m -u', addRetraction is also
called, and that will detect the retraction.

Fixes #53594

Change-Id: I90a2872cdeabf03894acad9e0cbdd7db4a4e269e
Reviewed-on: https://go-review.googlesource.com/c/go/+/414825
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>