Merge pull request #237 from govuk-forms/dependabot/github_actions/docker/setup-buildx-action-4.0.0

Bump docker/setup-buildx-action from 3.12.0 to 4.0.0

Author: lfdebrux

.github/workflows/docker_build.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-24.04-arm
     steps:
       - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f # v3.12.0
+        uses: docker/setup-buildx-action@4d04d5d9486b7bd6fa91e7baf45bbb4f8b9deedd # v4.0.0
 
       - name: Build
         uses: docker/build-push-action@10e90e3645eae34f1e60eeb005ba3a3d33f178e8 # v6.19.2