kde: kf6-kcrash + plasma-desktop — Qt6Test optional, grp.h for setgroups

- qtbase builds with FEATURE_testlib=OFF (no Qt6Test module), but kf6-kcrash and
  plasma-desktop find_package(Qt6Test REQUIRED) unconditionally though it's only
  used by autotests (BUILD_TESTING=OFF). Drop REQUIRED (kde-cli-tools/kwin already
  used QUIET).
- kcrash.cpp uses setgroups() to drop supplementary groups in the crash-handler
  child; on glibc it comes via <unistd.h>+_GNU_SOURCE, but relibc declares it in
  <grp.h> (which it does provide) — add the include.

local/recipes/kde/kf6-kcrash/source/CMakeLists.txt

@@ -34,7 +34,7 @@ if(WITH_X11)
     find_package(X11 REQUIRED)
     set(HAVE_X11 TRUE)
 endif()
-find_package(Qt6Test ${REQUIRED_QT_VERSION} CONFIG REQUIRED)
+find_package(Qt6Test ${REQUIRED_QT_VERSION} CONFIG)
 include(ECMGenerateExportHeader)
 include(ECMSetupVersion)
 include(ECMGenerateHeaders)

local/recipes/kde/kf6-kcrash/source/src/kcrash.cpp

@@ -24,6 +24,7 @@
 #include <qplatformdefs.h>
 #ifndef Q_OS_WIN
 #include <cerrno>
+#include <grp.h> // setgroups() — on glibc it comes via <unistd.h>+_GNU_SOURCE; relibc declares it in <grp.h>
 #include <sys/resource.h>
 #include <sys/un.h>
 #else

local/recipes/kde/plasma-desktop/source/CMakeLists.txt

@@ -96,7 +96,7 @@ find_package(PlasmaActivities ${PROJECT_DEP_VERSION} REQUIRED)
 find_package(PlasmaActivitiesStats ${PROJECT_DEP_VERSION} REQUIRED)
 
 if(BUILD_TESTING)
-    find_package(Qt6Test ${QT_MIN_VERSION} CONFIG REQUIRED)
+    find_package(Qt6Test ${QT_MIN_VERSION} CONFIG)
     include(ECMAddTests)
 endif()