Use mold linker for fedora CI builds

.docker/docker-qgis-build.sh

@@ -70,6 +70,12 @@ if [[ ${WITH_GRASS7} == "ON" || ${WITH_GRASS8} == "ON" ]]; then
   )
 fi
 
+if [[ ${BUILD_WITH_QT6} = "ON" ]]; then
+  CMAKE_EXTRA_ARGS+=(
+    "-DUSE_ALTERNATE_LINKER=mold"
+  )
+fi
+
 cmake \
  -GNinja \
  -DCMAKE_BUILD_TYPE=${BUILD_TYPE} \

.docker/qgis3-qt6-build-deps.dockerfile

@@ -32,6 +32,7 @@ RUN dnf -y --refresh install \
     libxml2-devel \
     libzip-devel \
     libzstd-devel \
+    mold \
     netcdf-devel \
     ninja-build \
     ocl-icd-devel \