docs: use webContents.mainFrame.on() in MessagePort tutorial (#35824)
docs: use webContents.mainFrame.on() in MessagePort tutorial (#35824)

* docs: use webContents.mainFrame.on() in MessagePort tutorial

* Update docs/tutorial/message-ports.md

Co-authored-by: Samuel Maddock <8775731458db809796e32a386b50b3006392c71f@salesforce.com>

Co-authored-by: Samuel Maddock <8775731458db809796e32a386b50b3006392c71f@salesforce.com>
gerhardberger/electron,electron/electron,gerhardberger/electron,electron/electron,electron/electron,gerhardberger/electron,gerhardberger/electron,electron/electron,gerhardberger/electron,electron/electron,electron/electron,electron/electron,gerhardberger/electron,gerhardberger/electron