mac: prepare desktop audio capture

With electron/electron#49717 the desktopCapturer
supports system audio for macOS 13 and above. Is was recently fixed
in electron/electron#49740 for current
electron.

This is a preparational step, but:

This on its own does not allow audio for screenshare, as its currently
hard-coded to only show the "Share Audio" button on windows, see
https://github.com/jitsi/jitsi-meet/blob/master/react/features/screen-share/functions.ts#L34

Author: csett86

package-lock.json

@@ -47,6 +47,7 @@
       "extendInfo": {
         "NSCameraUsageDescription": "Jitsi Meet requires access to your camera in order to make video-calls.",
         "NSMicrophoneUsageDescription": "Jitsi Meet requires access to your microphone in order to make calls (audio/video).",
+        "NSAudioCaptureUsageDescription": "Jitsi Meet can share your system audio via screensharing if you enable it.",
         "LSMultipleInstancesProhibited": true
       }
     },
@@ -153,7 +154,7 @@
     "babel-loader": "^8.2.3",
     "concurrently": "5.1.0",
     "css-loader": "^6.7.1",
-    "electron": "39.5.1",
+    "electron": "39.6.0",
     "electron-builder": "26.0.12",
     "electron-context-menu": "^2.5.0",
     "electron-is-dev": "^1.2.0",