LibJS: Change wording of ErrorType::NotA to be independent of context

Currently, we have NotA and NotAn, to be used dependent on whether the
following word begins with a vowel or not. To avoid this, change the
wording on NotA to be independent of this context.

Userland/Libraries/LibJS/Tests/builtins/Function/Function.prototype.bind.js

@@ -144,6 +144,6 @@ describe("errors", () => {
     test("does not accept non-function values", () => {
         expect(() => {
             Function.prototype.bind.call("foo");
-        }).toThrowWithMessage(TypeError, "Not a Function object");
+        }).toThrowWithMessage(TypeError, "Not an object of type Function");
     });
 });