Support macOS dark mode for UI

Fixes #4430

Thanks to ftpd for testing!

doc/changelog.asciidoc

@@ -125,6 +125,8 @@ Fixed
   certain workarounds) now works correctly on OpenBSD.
 - Certain version number formats in `/etc/os-release` caused qutebrowser to
   crash. Those are now handled correctly.
+- The macOS releases now properly support Dark Mode for UI elements by setting
+  `NSRequiresAquaSystemAppearance` to false.
 
 Removed
 ~~~~~~~

scripts/dev/build_release.py

@@ -260,6 +260,7 @@ INFO_PLIST_UPDATES = {
     'CFBundleShortVersionString': qutebrowser.__version__,
     'NSSupportsAutomaticGraphicsSwitching': True,
     'NSHighResolutionCapable': True,
+    'NSRequiresAquaSystemAppearance': False,
     'CFBundleURLTypes': [{
         "CFBundleURLName": "http(s) URL",
         "CFBundleURLSchemes": ["http", "https"]