Silence warning about Portage sandboxes

These don't work, and don't need to work, in a container.

.gitlab-ci.yml

@@ -17,6 +17,7 @@ default:
                    --security-opt seccomp=unconfined
                    --build-arg GENTOO_STAGE3_TAG="$GENTOO_ARCH"
                    --build-arg EMERGE_DEFAULT_OPTS="${CI_HOST_EMERGE_DEFAULT_OPTS} --usepkg"
+                   --build-arg FEATURES="-ipc-sandbox -pid-sandbox -network-sandbox"
                    --build-arg MAKEOPTS="$CI_HOST_MAKEOPTS"
                    --build-arg PROFILE="${CPU}/server"
                    -v "/usr/bin/qemu-${QEMU_ARCH}:/usr/bin/qemu-${QEMU_ARCH}:ro"

Containerfile

@@ -4,6 +4,7 @@ FROM nest/gentoo/portage AS gentoo-portage
 FROM nest/gentoo/stage3:${GENTOO_STAGE3_TAG}
 
 ARG EMERGE_DEFAULT_OPTS
+ARG FEATURES
 ARG MAKEOPTS
 ARG PROFILE