Edit configuration in "offline" mode when starting Electrum

Otherwise this command fails because "Daemon not running",
and thus we abort our wrapper script and Electrum won't start.

refs #17828

config/chroot_local-includes/usr/local/bin/electrum

@@ -35,7 +35,7 @@ def main(*args):
     # Disable update checking for all users (even those who made their config
     # persistent before we changed this value in the default config), because
     # users can't easily update to a new version anyway if it's not in Debian.
-    subprocess.run(['/usr/bin/electrum', 'setconfig', 'check_updates', 'false'], check=True, stdout=subprocess.DEVNULL)
+    subprocess.run(['/usr/bin/electrum', '--offline', 'setconfig', 'check_updates', 'false'], check=True, stdout=subprocess.DEVNULL)
     os.execv('/usr/bin/electrum', ['/usr/bin/electrum'] + list(args))