spec: robustify sendInputEvent beforeEach hook (#17340)

spec/api-web-contents-spec.js

@@ -424,9 +424,8 @@ describe('webContents module', () => {
   })
 
   describe('sendInputEvent(event)', () => {
-    beforeEach((done) => {
-      w.webContents.once('did-finish-load', () => done())
-      w.loadFile(path.join(fixtures, 'pages', 'key-events.html'))
+    beforeEach(async () => {
+      await w.loadFile(path.join(fixtures, 'pages', 'key-events.html'))
     })
 
     it('can send keydown events', (done) => {