manifest: Re-upgrade Qt to 5.15.2
The previous update of the dunfell layers accidentally downgraded Qt to Qt 5.14.2 in cae66845.
Revert this by pulling the version 41c0d8d277c76b0fda423f2aaa794d3f3889ce99 from the Qt project again.
Change-Id: I0a728422e5c2a68027e3c102f643f2f0cad77ab2