flatpak template: fix used BUILD_TESTING flag
The flag used in KDE projects usually is called BUILD_TESTING, not ENABLE_TESTING, as set by KDECMakeSettings (& the CTest module).
Edited by Friedrich W. H. Kossebau
The flag used in KDE projects usually is called BUILD_TESTING, not ENABLE_TESTING, as set by KDECMakeSettings (& the CTest module).