python-marshmallow: fix missing host-build dependencies

python-marshmallow: fix missing host-build dependencies

When python3 -m build is invoked during host-compile, it fails with:

  /builder/staging_dir/hostpkg/bin/python3.14: No module named build

The package's HOST_BUILD_DEPENDS only pulled in python3 and
python-packaging, missing the actual host tooling for the new
pyproject build flow:

  - python-build      : provides the 'build' module itself
  - python-installer  : installs the resulting wheel
  - python-wheel      : wheel format support
  - python-flit-core  : marshmallow's declared build-backend
                        (build-backend = "flit_core.buildapi" in
                        pyproject.toml)

Signed-off-by: Alexandru Ardelean <redacted>