qt: Remove QFont warnings with QPA=minimal
Summary: This is a backport of core#17908
Test Plan:
Before this patch:
$ ./src/qt/test/test_bitcoin-qt | grep QFont | wc -l ~BitcoinApplication : Stopping thread ~BitcoinApplication : Stopped thread 17
After:
$ ./src/qt/test/test_bitcoin-qt | grep QFont | wc -l ~BitcoinApplication : Stopping thread ~BitcoinApplication : Stopped thread 0
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Subscribers: majcosta
Differential Revision: https://reviews.bitcoinabc.org/D9924