Allow Spectacle to build with KConfig <= 5.56.0

Summary: D22040 broke the build of Spectacle with KConfig <= 5.56.0, because older KConfig needs Q_FOREACH.  5.53.0 is still the target KF5 version for Spectacle 19.08.

Test Plan: Tested on KConfig 5.54.0 (the last version that works with Qt 5.9 LTS).  Builds and runs correctly.

Reviewers: davidre, #spectacle, ngraham

Reviewed By: #spectacle, ngraham

Subscribers: ngraham, #spectacle

Tags: #spectacle

Differential Revision: https://phabricator.kde.org/D23176