Revert "fix .kde-ci.yml"
Stump branch, forked off at the commit "Port from Grantlee to KTextTemplate" which needs to be replaced by the new variant in this branch.
To get rid of the commit "fix .kde-ci.yml" which wrongly tried to use inofficial grantlee/qt6 while actually with Qt6 KTextTemplate is to be used.
First commit is to undo the change that the to-be-dropped commit did.
Second commit is the existing one adopted to the conflict in .kde-ci.yml, to be used to replace the current one after that other commit is removed.