Currently Openpyxl cannot properly read stylesheets which contain valid but non-contiguous xfId's in the
<cellStyles> elements. In the process of renumbering the xfId's, the incoming style information is lost. This MR moves responsibility for renumbering the xfId's from the _NamedStyleCellList.names() method to the Stylesheet._merge_named_styles() method, which allows Stylesheet._expand_named_style() to work as intended.
See also #1457 (comment 329545) for an example.
The "pypy3" and "python312" failed CI tests are unrelated to any changes being made here.
--HG-- branch : 3.1