ci: use updated docs-builder image
ci: use updated docs-builder image

To test the Sphinx updates, use an up-to-date image for building the
documentation in the GitHub workflow.

Joe kindly generated the new image from the tip of the PR (before this
commit was updated).

Signed-off-by: Quentin Monnet <d6b8e48afb2534b213e391cab43016505747a234@isovalent.com>

michi-covalent/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium