go/types, types2: fix Hilbert test for stand-alone run
When run as a stand-alone test (without other tests running before),
the builtin function 'assert' (only available for testing) is missing.
Make sure it's declared.
This change only affects this test, when run stand-alone, as in:
go test -run Hilbert
Fixes #60774.
Change-Id: Ib07d97ba2670b839e8ad11ef50d0e6581bb3d79d
Reviewed-on: https://go-review.googlesource.com/c/go/+/502996
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com> Reviewed-by: Robert Griesemer <gri@google.com>