fix(gnovm): detect invalid interface implementation with name collision (#4862)

An struct containing a field matching an interface method name could be
wrongly seen as implementing such interface.

The corresponding type check was performed only for functions. Now also
catch non function types.

Fixes GHSA-v84r-rg57-8j33

Author: mvertes

gnovm/pkg/gnolang/types.go

@@ -1050,6 +1050,8 @@ func (it *InterfaceType) VerifyImplementedBy(ot Type) error {
 			if dmtid != imtid {
 				return fmt.Errorf("wrong type for method %s", im.Name)
 			}
+		} else {
+			return fmt.Errorf("wrong type for method %s", im.Name)
 		}
 	}
 	return nil

gnovm/tests/files/types/assign_iface.gno

@@ -0,0 +1,20 @@
+package main
+
+type MyStruct struct {
+    doSomething int // only name matches the interface
+}
+
+type MyInterface interface {
+    doSomething(string) string
+}
+
+func main() {
+    var x MyInterface = MyStruct{}
+    println("ok", x == nil)
+}
+
+// Error:
+// main/assign_iface.gno:12:9-35: main.MyStruct does not implement main.MyInterface (wrong type for method doSomething)
+
+// TypeCheckError:
+// main/assign_iface.gno:12:25: cannot use MyStruct{} (value of struct type MyStruct) as MyInterface value in variable declaration: MyStruct does not implement MyInterface (MyStruct.doSomething is a field, not a method)