ecm.eclass: Restrict ECM_QTHELP to <6.15 for KDE Frameworks

6.15 changes how API documentation is built, and we haven't implemented
it yet.

See also:
https://mail.kde.org/pipermail/distributions/2025-June/001595.html

Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>

eclass/ecm.eclass

@@ -126,7 +126,7 @@ fi
 # If set to "true", add "doc" to IUSE, add the appropriate dependency, let
 # -DBUILD_QCH=ON generate and install Qt compressed help files when USE=doc.
 # If set to "false", do nothing.
-if [[ ${CATEGORY} = kde-frameworks ]]; then
+if [[ ${CATEGORY} = kde-frameworks ]] && ver_test -lt 6.15; then
 	: "${ECM_QTHELP:=true}"
 fi
 : "${ECM_QTHELP:=false}"