build: copy a newer version of ax_code_coverage.m4, still unmodified
build: copy a newer version of ax_code_coverage.m4, still unmodified

From autoconf-archive 2022.02.11.

The purpose is to modify it, to fix a bug (a warning), and to clearly
see the diff in the next commit.

GNOME/gspell,GNOME/gspell