tools: Fix groupname if it differs from username

The script `tools/packaging/static-build/qemu/build-base-qemu.sh`
previously failed on systems where the user's groupname differs from the
username

Fixes: #3461

Signed-off-by: Sebastian Hasler <sebastian.hasler@stuvus.uni-stuttgart.de>

tools/packaging/static-build/qemu/build-base-qemu.sh

@@ -54,4 +54,4 @@ sudo "${container_engine}" run \
 	-v "${PWD}":/share qemu-static \
 	mv "${qemu_destdir}/${qemu_tar}" /share/
 
-sudo chown ${USER}:${USER} "${PWD}/${qemu_tar}"
+sudo chown ${USER}:$(id -gn ${USER}) "${PWD}/${qemu_tar}"