Slightly tweak the not-unit Ltac2 warning.
Slightly tweak the not-unit Ltac2 warning.

Fixes #11683.

coq/coq,JasonGross/coq,SkySkimmer/coq,coq/coq,SkySkimmer/coq,Zimmi48/coq,Zimmi48/coq,coq/coq,ejgallego/coq,ejgallego/coq,JasonGross/coq,JasonGross/coq,JasonGross/coq,coq/coq,ejgallego/coq,Zimmi48/coq,Zimmi48/coq,SkySkimmer/coq,ejgallego/coq,SkySkimmer/coq