Fix test: "No OpEntryPoint instruction was found"

Bug found when passing program through spirv writer and then reader.

Bug: tint:792
Change-Id: I2acb17554b122c840cf3cc69149f6e004fb37bc7
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50562
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/resolver/host_shareable_validation_test.cc

@@ -143,6 +143,7 @@ TEST_F(ResolverHostShareableValidationTest, NoError) {
              create<ast::BindingDecoration>(0),
              create<ast::GroupDecoration>(0),
          });
+  WrapInFunction();
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
 }