fix: Explicitly mark async calls as void

Avoids `no-floating-promises` warning from eslint
<https://typescript-eslint.io/rules/no-floating-promises/>.

src/__test__/index.test.ts

@@ -3,8 +3,8 @@ import { describe, it } from 'node:test';
 
 import { helloWorld } from '../index.js';
 
-describe('helloWorld', () => {
-  it('should respond with hello world', () => {
+void describe('helloWorld', () => {
+  void it('should respond with hello world', () => {
     assert.equal(helloWorld('test'), 'hello world! test');
   });
 });