ci: fix context for disabled docker images

When the dockerfiles were moved into the host-x86_64 directory, paths
for COPY commands were updated with the new host-x86_64/ prefix. This
suggested that the intended context was src/ci/docker. However, the context
for disabled docker images was src/ci/docker/host-x86_64. This broke the new
paths and prevented src/ci/docker/scripts from being included in the
context at all.

This commit corrects this context allowing docker to find the files it
needs for COPY commands.

src/ci/docker/run.sh

@@ -119,11 +119,11 @@ elif [ -f "$docker_dir/disabled/$image/Dockerfile" ]; then
         exit 1
     fi
     # Transform changes the context of disabled Dockerfiles to match the enabled ones
-    tar --transform 's#^./disabled/#./#' -C $docker_dir -c . | docker \
+    tar --transform 's#disabled/#./#' -C $script_dir -c . | docker \
       build \
       --rm \
       -t rust-ci \
-      -f "$image/Dockerfile" \
+      -f "host-$(uname -m)/$image/Dockerfile" \
       -
 else
     echo Invalid image: $image