Another fix for TypeUtils#isAssignable()

A type like `List<? extends String>` is not assignable to e.g. `List<String>` (without cast).

rewrite-java/src/main/java/org/openrewrite/java/tree/TypeUtils.java

@@ -213,7 +213,7 @@ public static boolean isAssignableTo(@Nullable JavaType to, @Nullable JavaType f
                         return true;
                     }
                 }
-                return isAssignableTo(toFq.getFullyQualifiedName(), from);
+                return !(from instanceof JavaType.GenericTypeVariable) && isAssignableTo(toFq.getFullyQualifiedName(), from);
             } else if (to instanceof JavaType.GenericTypeVariable) {
                 JavaType.GenericTypeVariable toGeneric = (JavaType.GenericTypeVariable) to;
                 List<JavaType> toBounds = toGeneric.getBounds();