depends: Bump QT to LTS release 5.9.8
Summary:
This update is only a minor version but in contrary to 5.9.7 it's a LTS release. It doesn't add any new functionality to Qt but fixes multiple security issues and bugs. Including some race conditions and annoying bugs on macOS.
Backport of core PR16413.
Test Plan: Run the Gitian builds.
Reviewers: #bitcoin_abc, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Subscribers: jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D5643