fix(preload): whitelist monospace-setting-change channel

Reviewer caught that the new View > Monospace Font menu channel was
missing from preload.js's ALLOWED_RECEIVE_CHANNELS, the sole gap among
29 raw ipcRenderer.on(...) channels used in renderer.js. Add it under
the existing Font section for consistency with adjust-font-size.

Amit Haridas

src/preload.js

@@ -172,6 +172,7 @@ const ALLOWED_RECEIVE_CHANNELS = [
 
   // Font
   'adjust-font-size',
+  'monospace-setting-change',
 
   // Print
   'print-preview',