Revert "FIXME: disable isCurrentlyAudible test to unblock merge" (#15083)

This reverts commit c8a9a3f63c25f983aeb0067ac88534c9b752e144.

spec/api-web-contents-spec.js

@@ -125,9 +125,7 @@ describe('webContents module', () => {
     })
   })
 
-  // FIXME: this is broken on mac in the M69 upgrade, fix & re-enable before
-  // release
-  xdescribe('isCurrentlyAudible() API', () => {
+  describe('isCurrentlyAudible() API', () => {
     it('returns whether audio is playing', async () => {
       const webContents = remote.getCurrentWebContents()
       const context = new window.AudioContext()