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/Temporal/Instant/Instant.fromEpochMilliseconds.js

@@ -24,7 +24,7 @@ describe("correct behavior", () => {
     });
 });
 
-test("errors", () => {
+describe("errors", () => {
     test("argument must be coercible to BigInt", () => {
         expect(() => {
             Temporal.Instant.fromEpochMilliseconds(1.23);