Bump buildx and limit max parallel builds (#5579)

.cspell.json

@@ -30,6 +30,7 @@
     "bradrydzewski",
     "BUILDPLATFORM",
     "buildx",
+    "buildkit",
     "caddyfile",
     "ccmenu",
     "CERTDIR",

.woodpecker/docker.yaml

@@ -2,7 +2,7 @@ variables:
   - &golang_image 'docker.io/golang:1.25'
   - &node_image 'docker.io/node:23-alpine'
   - &xgo_image 'docker.io/techknowlogick/xgo:go-1.25.x'
-  - &buildx_plugin 'docker.io/woodpeckerci/plugin-docker-buildx:6.0.2'
+  - &buildx_plugin 'docker.io/woodpeckerci/plugin-docker-buildx:6.0.3'
   - &platforms_release 'linux/arm/v6,linux/arm/v7,linux/arm64/v8,linux/386,linux/amd64,linux/ppc64le,linux/riscv64,linux/s390x,freebsd/arm64,freebsd/amd64,openbsd/arm64,openbsd/amd64'
   - &platforms_server 'linux/arm/v7,linux/arm64/v8,linux/amd64,linux/ppc64le,linux/riscv64'
   - &platforms_preview 'linux/amd64'
@@ -243,6 +243,7 @@ steps:
       repo: *publish_repos_agent
       dockerfile: docker/Dockerfile.agent.multiarch
       platforms: *platforms_release
+      buildkit_oci_max_parallelism: 6
       tag: [next, 'next-${CI_COMMIT_SHA:0:10}']
       logins: *publish_logins
       build_args: *build_args
@@ -278,6 +279,7 @@ steps:
       repo: *publish_repos_agent
       dockerfile: docker/Dockerfile.agent.multiarch
       platforms: *platforms_release
+      buildkit_oci_max_parallelism: 6
       tag: ['${CI_COMMIT_TAG%%.*}', '${CI_COMMIT_TAG%.*}', '${CI_COMMIT_TAG}']
       logins: *publish_logins
       build_args: *build_args
@@ -327,6 +329,7 @@ steps:
       repo: *publish_repos_cli
       dockerfile: docker/Dockerfile.cli.multiarch.rootless
       platforms: *platforms_release
+      buildkit_oci_max_parallelism: 6
       tag: [next, 'next-${CI_COMMIT_SHA:0:10}']
       logins: *publish_logins
       build_args: *build_args
@@ -359,6 +362,7 @@ steps:
       repo: *publish_repos_cli
       dockerfile: docker/Dockerfile.cli.multiarch.rootless
       platforms: *platforms_release
+      buildkit_oci_max_parallelism: 6
       tag: ['${CI_COMMIT_TAG%%.*}', '${CI_COMMIT_TAG%.*}', '${CI_COMMIT_TAG}']
       logins: *publish_logins
       build_args: *build_args