SUMMARY
Since updating to 5.15.0, the 'Use 24-hour Clock' option in the Digital Clock plasmoid's settings does not work anymore and the clock always shows 12h format in en_US locale.

STEPS TO REPRODUCE
1. Choose locale with 12h format.
2. Open settings of Digital Clock plasmoid
3. Check the 'Use 24-hour Clock' checkbox and apply settings

OBSERVED RESULT
The time is shown in 12h AM/PM format.

EXPECTED RESULT
The time is shown in 24h format.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.15.0
KDE Frameworks Version: 5.55.0
Qt Version: 5.12.1

ADDITIONAL INFORMATION
This is a regression from the last stable release.