[libc++][docs] Update status for P2641R4 (#166073)

Follows-up 2527b07 which missed
updating the status in the documentations.

Author: frederick-vs-ja

libcxx/docs/ReleaseNotes/22.rst

@@ -43,6 +43,8 @@ Implemented Papers
 - P3044R2: sub-``string_view`` from ``string`` (`Github <https://llvm.org/PR148140>`__)
 - P3223R2: Making ``std::istream::ignore`` less surprising (`Github <https://llvm.org/PR148178>`__)
 - P3060R3: Add ``std::views::indices(n)`` (`Github <https://llvm.org/PR148175>`__)
+- P2641R4: Checking if a ``union`` alternative is active (``std::is_within_lifetime``)
+  (`Github <https://llvm.org/PR105381>`__)
 - P2835R7: Expose ``std::atomic_ref``'s object address (`Github <https://llvm.org/PR118377>`__)
 - P2944R3: Comparisons for ``reference_wrapper`` (`Github <https://llvm.org/PR105424>`__)
 - P3168R2: Give ``std::optional`` Range Support (`Github <https://llvm.org/PR105430>`__)

libcxx/docs/Status/Cxx2cPapers.csv

@@ -18,7 +18,7 @@
 "`P2874R2 <https://wg21.link/P2874R2>`__","P2874R2: Mandating Annex D Require No More","2023-06 (Varna)","|Complete|","12","`#105377 <https://github.com/llvm/llvm-project/issues/105377>`__",""
 "`P2757R3 <https://wg21.link/P2757R3>`__","Type-checking format args","2023-06 (Varna)","","","`#105378 <https://github.com/llvm/llvm-project/issues/105378>`__",""
 "`P2637R3 <https://wg21.link/P2637R3>`__","Member ``visit``","2023-06 (Varna)","|Complete|","19","`#105380 <https://github.com/llvm/llvm-project/issues/105380>`__","Change of ``__cpp_lib_variant`` is completed in LLVM 20. Change of ``__cpp_lib_format`` is blocked by `P2419R2 <https://wg21.link/P2419R2>`__."
-"`P2641R4 <https://wg21.link/P2641R4>`__","Checking if a ``union`` alternative is active","2023-06 (Varna)","","","`#105381 <https://github.com/llvm/llvm-project/issues/105381>`__",""
+"`P2641R4 <https://wg21.link/P2641R4>`__","Checking if a ``union`` alternative is active","2023-06 (Varna)","|Complete|","22","`#105381 <https://github.com/llvm/llvm-project/issues/105381>`__",""
 "`P1759R6 <https://wg21.link/P1759R6>`__","Native handles and file streams","2023-06 (Varna)","|Complete|","18","`#105382 <https://github.com/llvm/llvm-project/issues/105382>`__",""
 "`P2697R1 <https://wg21.link/P2697R1>`__","Interfacing ``bitset`` with ``string_view``","2023-06 (Varna)","|Complete|","18","`#105384 <https://github.com/llvm/llvm-project/issues/105384>`__",""
 "`P1383R2 <https://wg21.link/P1383R2>`__","More ``constexpr`` for ``<cmath>`` and ``<complex>``","2023-06 (Varna)","","","`#105385 <https://github.com/llvm/llvm-project/issues/105385>`__",""