Update docker/metadata-action action to v6 (#65)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/release.yml

@@ -42,7 +42,7 @@ jobs:
 
       - name: Extract metadata
         id: meta
-        uses: docker/metadata-action@c299e40c65443455700f0fdfc63efafe5b349051 # v5.10.0
+        uses: docker/metadata-action@030e881283bb7a6894de51c315a6bfe6a94e05cf # v6.0.0
         with:
           images: ghcr.io/${{ steps.repo_owner.outputs.OWNER }}/plotting-mcp
           tags: |