Mark test.EquateErrors as deprecated

See crossplane/crossplane#4514 for context.

We can't remove this (it would be a breaking API change) but I want to
discourage and redirect folks.

Signed-off-by: Nic Cope <[email protected]>

Author: negz

pkg/test/cmp.go

@@ -33,6 +33,8 @@ import (
 // This differs from cmpopts.EquateErrors, which does not test for error strings
 // and instead returns whether one error 'is' (in the errors.Is sense) the
 // other.
+//
+// Deprecated: Use cmpopts.EquateErrors instead.
 func EquateErrors() cmp.Option {
 	return cmp.Comparer(func(a, b error) bool {
 		if a == nil || b == nil {