python310Packages.pydantic: fix using lib.optionalString

  # Must include current directory into PYTHONPATH, since documentation

  # building process expects "import pydantic" to work.

  preBuild = lib.optionals withDocs ''

  preBuild = lib.optionalString withDocs ''

    PYTHONPATH=$PWD:$PYTHONPATH make docs

  '';

  # Layout documentation in same way as "sphinxHook" does.

  postInstall = lib.optionals withDocs ''

  postInstall = lib.optionalString withDocs ''

    mkdir -p $out/share/doc/$name

    mv ./site $out/share/doc/$name/html

  '';