fix: all build cache mirrors equal now

containers/jug/dev.Dockerfile

@@ -63,8 +63,8 @@ RUN declare -A target=(                                                 \
 
 ## Setup spack buildcache mirrors
 RUN --mount=type=cache,target=/var/cache/spack-mirror                   \
-    spack mirror add docker /var/cache/spack-mirror                     \
- && spack buildcache update-index -d /var/cache/spack-mirror            \
+    spack mirror add spack-mirror /var/cache/spack-mirror               \
+ && spack buildcache update-index -m spack-mirror                       \
  && spack mirror list
 
 ## Setup eic-spack buildcache mirrors
@@ -112,8 +112,7 @@ RUN --mount=type=cache,target=/ccache,id=${TARGETPLATFORM}              \
  && spack env activate --dir ${SPACK_ENV}                               \
  && make --jobs ${jobs} --keep-going --directory /opt/spack-environment \
     SPACK_ENV=${SPACK_ENV}                                              \
-    BUILDCACHE_DIR=/var/cache/spack-mirror                              \
-    BUILDCACHE_MIRROR=eic-spack                                         \
+    BUILDCACHE_MIRROR="spack-mirror eic-spack"                                         \
  && ccache --show-stats
 
 ## Create view at /usr/local