keepassxc: run test with offscreen qt plugin

Co-Authored-By: Quiark <me@rplasil.name>

pkgs/applications/misc/keepassx/community.nix

@@ -69,7 +69,8 @@ stdenv.mkDerivation rec {
   doCheck = true;
   checkPhase = ''
     export LC_ALL="en_US.UTF-8"
-	export QT_PLUGIN_PATH="${qtbase.bin}/${qtbase.qtPluginPrefix}"
+    export QT_PLUGIN_PATH="${qtbase.bin}/${qtbase.qtPluginPrefix}"
+    export QT_QPA_PLATFORM=offscreen
     make test ARGS+="-E testgui --output-on-failure"
   '';