[Bug c++/96926] [9/10/11 Regression] Tuple element w/ member reference to incomplete template type rejected

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96926

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Created attachment 49180
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49180&action=edit
Manually reduced code