syntax highlighting string interpolation

[EmilienMottet]

I have a similar syntax error like the #369

A string interpolation into a call of function into another string interpolation break syntax highlighting

OS : gentoo
elixir-mode : 20190422.155
emacs : GNU Emacs 26.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.7) of 2019-04-13