Fix remaining Qt 6 snap issues

[furgo16]

• Warning: Failed to create wl_display (No such file or directory): See https://forum.snapcraft.io/t/kde-neon-6-extension-snap-qt-qpa-platform-overwritten/46054/8
• Warning: Qt: Session management error: Could not open network socket
• Warnings:

  Warning: Schema “org.gnome.system.locale” has path “/system/locale/”.  Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
  Warning: Schema “org.gnome.system.proxy” has path “/system/proxy/”.  Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
  Warning: Schema “org.gnome.system.proxy.http” has path “/system/proxy/http/”.  Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
  Warning: Schema “org.gnome.system.proxy.https” has path “/system/proxy/https/”.  Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
  Warning: Schema “org.gnome.system.proxy.ftp” has path “/system/proxy/ftp/”.  Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
  Warning: Schema “org.gnome.system.proxy.socks” has path “/system/proxy/socks/”.  Paths starting with “/apps/”, “/desktop/” or “/system/” are deprecated.
  
  

[furgo16]

At this point, and pending testing, the two critical sub-issues have been fixed. The warnings appear to be unharmful.