[spack] Use signing key for buildcache

Author: cedricchevalier19

.github/workflows/docker-publish.yml

@@ -94,3 +94,5 @@ jobs:
           push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
+          secrets: |
+            "signingkey=${{ secrets.BUILDCACHE_PRIVATE_KEY }}"

spack/Dockerfile

@@ -28,7 +28,7 @@ RUN mkdir -p recipes && \
 
 ADD import_signing_key.sh /tmp
 
-RUN --mount=type=secret,id=signingkey,uid=1000 /tmp/import_signing_key.sh /run/secrets/signingkey
+RUN --mount=type=secret,id=signingkey /tmp/import_signing_key.sh /run/secrets/signingkey
 
 FROM base AS builder