Switch to buildah for the foreign document test.

BuildKit is having issues with caching which is causing problems with long builds like compiling emacs from source.

docker/organic_test/Dockerfile

@@ -19,7 +19,17 @@ RUN apk add --no-cache build-base musl-dev git autoconf make texinfo gnutls-dev
 FROM build AS build-emacs
 ARG EMACS_REPO
 ARG EMACS_VERSION
-ADD "$EMACS_REPO#$EMACS_VERSION" /root/emacs
+
+RUN <<EOF
+set -euo pipefail
+IFS=$'\n\t'
+mkdir -p /root/emacs
+git -C /root/emacs init --initial-branch=main
+git -C /root/emacs remote add origin $EMACS_REPO
+git -C /root/emacs fetch origin $EMACS_VERSION
+git -C /root/emacs checkout FETCH_HEAD
+EOF
+#ADD "$EMACS_REPO#$EMACS_VERSION" /root/emacs
 WORKDIR /root/emacs
 RUN <<EOF
 mkdir /root/dist