LibJS/Tests: Fix bad copy and paste that crept into a lot of tests

The top-level function should have been `describe()``, but instead it's
been nested `test()`s.

Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.toFixed.js

@@ -26,7 +26,7 @@ describe("correct behavior", () => {
     });
 });
 
-test("errors", () => {
+describe("errors", () => {
     test("must be called with numeric |this|", () => {
         [true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {
             expect(() => Number.prototype.toFixed.call(value)).toThrowWithMessage(

Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.toString.js

@@ -72,7 +72,7 @@ describe("correct behavior", () => {
     });
 });
 
-test("errors", () => {
+describe("errors", () => {
     test("must be called with numeric |this|", () => {
         [true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {
             expect(() => Number.prototype.toString.call(value)).toThrowWithMessage(

Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.valueOf.js

@@ -9,7 +9,7 @@ describe("correct behavior", () => {
     });
 });
 
-test("errors", () => {
+describe("errors", () => {
     test("must be called with numeric |this|", () => {
         [true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {
             expect(() => Number.prototype.valueOf.call(value)).toThrowWithMessage(