docs(deps[gp-sphinx]) Refresh lock to pull reftype=obj fix

why: gp-sphinx PR #36 commit `efd4b12` switches the default-value
cross-reference transform from `reftype="class"` to `reftype="obj"`,
so module-level data attributes (like libtmux's
`DEFAULT_OPTION_SCOPE`) now resolve and render as clickable links
instead of misleading-styled unresolved spans. The lock previously
pinned `8c3a1418` (Stage C with the broken class-only reftype); this
refresh moves every gp-sphinx-family entry forward to `efd4b12`.

what:
- Re-resolve every gp-sphinx-family git source (`gp-sphinx`,
  `sphinx-autodoc-typehints-gp`, `sphinx-autodoc-api-style`,
  `sphinx-autodoc-pytest-fixtures`, plus the transitive workspace
  siblings sphinx-fonts, sphinx-gp-{opengraph,sitemap,theme},
  sphinx-ux-{autodoc-layout,badges}, gp-furo-theme) at commit
  `efd4b12`. No other deps move.

Author: tony