fix: avoid locking local spack build cache

This does not appear to be necessary. It was introduced as a way to resolve the exec format errors which were due eager qemu binfmt resets.

containers/jug/dev.Dockerfile

@@ -102,7 +102,7 @@ RUN git clone https://github.com/${EICSPACK_ORGREPO}.git ${EICSPACK_ROOT}     \
 COPY --from=spack spack-environment/ /opt/spack-environment/
 ARG ENV=dev
 ENV SPACK_ENV=/opt/spack-environment/${ENV}
-RUN --mount=type=cache,target=/var/cache/spack-mirror,sharing=locked    \
+RUN --mount=type=cache,target=/var/cache/spack-mirror                   \
     --mount=type=secret,id=mirrors,target=/opt/spack/etc/spack/mirrors.yaml \
     source $SPACK_ROOT/share/spack/setup-env.sh                         \
  && spack env activate --dir ${SPACK_ENV}                               \
@@ -112,7 +112,7 @@ RUN --mount=type=cache,target=/var/cache/spack-mirror,sharing=locked    \
     BUILDCACHE_MIRROR=eic-spack
 
 ## Create view at /usr/local
-RUN --mount=type=cache,target=/var/cache/spack-mirror,sharing=locked    \
+RUN --mount=type=cache,target=/var/cache/spack-mirror                   \
     source $SPACK_ROOT/share/spack/setup-env.sh                         \
  && spack env activate --dir ${SPACK_ENV}                               \
  && rm -r /usr/local                                                    \