Always exclude inigrep from debugging

It makes a lot of noise that is normally not very relevant to the
application.

src/bin/app.skel

     SATURNIN_LIBEXEC_PREFIX="__MKIT_PROJ_PKGNAME__-"
     SHELLFU_PATH="__SATURNIN_SHELLFU_DIR__"
     PRETTY_USAGE="subcommand"
+    PRETTY_DEBUG_EXCLUDE="$PRETTY_DEBUG_EXCLUDE:inigrep"
 }
 
 shellfu import saturnin