Update docker/setup-buildx-action action to v3.12.0 (#603)

| datasource  | package                    | from    | to      |
| ----------- | -------------------------- | ------- | ------- |
| github-tags | docker/setup-buildx-action | v3.11.1 | v3.12.0 |

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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -65,7 +65,7 @@ jobs:
           sed -i 's|\${NGINX_PLUS_VERSION}/||g' docker/Dockerfile
 
       - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@e468171a9de216ec08956ac3ada2f0791b6bd435 # v3.11.1
+        uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f # v3.12.0
 
       - name: Build Plus Docker Image
         uses: docker/build-push-action@263435318d21b8e681c14492fe198d362a7d2c83 # v6.18.0