FFmpeg version was between n6.0 and n6.1 due to some hotfix
for having it compilable on CI. Since n6.1 has been released,
we should update.
Task-number: QTBUG-121441
Pick-to: 6.7 6.6 6.5 dev
Change-Id: I0d88599be53748eeb038287abe8aad6c0f189933
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>