gentoo: use new official binpkg host

* Use new official binpkg host (https://www.gentoo.org/news/2023/12/29/Gentoo-binary.html)
* Require signed binpkgs

Signed-off-by: Sam James <sam@gentoo.org>

gentoo/Dockerfile

@@ -4,12 +4,11 @@ FROM gentoo/stage3:desktop
 RUN echo 'FEATURES="-ipc-sandbox -pid-sandbox -network-sandbox -usersandbox -mount-sandbox -sandbox"' | cat >> /etc/portage/make.conf
 # Speed things up a bit.
 RUN echo 'FEATURES="${FEATURES} parallel-install parallel-fetch -merge-sync"' | cat >> /etc/portage/make.conf
+# We use binpkgs.
+RUN echo 'FEATURES="${FEATURES} getbinpkg binpkg-request-signature"' | cat >> /etc/portage/make.conf
+RUN getuto
 
-# TODO: May be able to drop this once changed to desktop docker images?
-# https://dilfridge.blogspot.com/2021/09/experimental-binary-gentoo-package.html
-RUN echo -e "[gentoobinhost]\npriority = 9999\nsync-uri = https://gentoo.osuosl.org/experimental/amd64/binpkg/default/linux/17.1/x86-64/\n" | cat >> /etc/portage/binrepos.conf/gentoobinhost.conf
-
-RUN echo 'EMERGE_DEFAULT_OPTS="--binpkg-respect-use=n --getbinpkg=y --autounmask-write --autounmask-continue --autounmask-keep-keywords=y --autounmask-use=y"' | cat >> /etc/portage/make.conf
+RUN echo 'EMERGE_DEFAULT_OPTS="--binpkg-respect-use=n --autounmask-write --autounmask-continue --autounmask-keep-keywords=y --autounmask-use=y"' | cat >> /etc/portage/make.conf
 RUN echo 'USE="elogind -polkit"' | cat >> /etc/portage/make.conf
 RUN cat /etc/portage/make.conf