For each include line referencing a _py39 file or directory in docs_src, replace
    the _py39 label with _py310.
    """
    include_pattern = re.compile(r"\{[^}]*docs_src/[^}]*_py39[^}]*\.py[^}]*\}")
    count = 0
    for md_file in sorted(en_docs_path.rglob("*.md")):
        content = md_file.read_text(encoding="utf-8")
        if "_py39" not in content: