tox.ini (docker): Make DOCKER_BUILDKIT=1 the default

Author: Matthias Koeppe

tox.ini

@@ -143,7 +143,7 @@ passenv =
     docker:       EXTRA_DOCKER_BUILD_ARGS
     docker:       EXTRA_DOCKER_TAGS
     docker:       DOCKER_TAG
-                  # Use DOCKER_BUILDKIT=1 for new version - for which unfortunately we cannot save failed builds as an image
+                  # Use DOCKER_BUILDKIT=0 for legacy builder
     docker:       DOCKER_BUILDKIT
     docker:       BUILDKIT_INLINE_CACHE
                   # Set for example to "with-system-packages configured with-targets-pre with-targets"
@@ -756,7 +756,7 @@ commands =
     docker:            BUILD_IMAGE=$DOCKER_PUSH_REPOSITORY$BUILD_IMAGE_STEM-$docker_target; \
     docker:            BUILD_TAG={env:DOCKER_TAG:$(git describe --dirty --always)}; \
     docker:            TAG_ARGS=$(for tag in $BUILD_TAG {env:EXTRA_DOCKER_TAGS:}; do echo --tag $BUILD_IMAGE:$tag; done); \
-    docker:            DOCKER_BUILDKIT={env:DOCKER_BUILDKIT:0}; \
+    docker:            DOCKER_BUILDKIT={env:DOCKER_BUILDKIT:1}; \
     docker:            docker build . -f {envdir}/Dockerfile \
     docker:              --target $docker_target \
     docker:              $TAG_ARGS \