fix various shellcheck issues

src/shared/die.sh

···
 function atfile.die() {
     message="$1"
 
+    # shellcheck disable=SC2154
     if [[ $_output_json != 1 ]]; then
         atfile.say.die "$message"
     else
         echo -e "{ \"error\": \"$1\" }" | jq
     fi
     
+    # shellcheck disable=SC2154
     [[ $_is_sourced == 0 ]] && exit 255
 }
 
···
 
 function atfile.die.unknown_command() {
     command="$1"
-    atfile.die "Unknown command '$1'"
+    atfile.die "Unknown command '$command'"
 }

src/shared/invoke.sh

···
     shift
     args=("$@")
 
+    # shellcheck disable=SC2154
     if [[ $_is_sourced == 0 ]] && [[ $ATFILE_DEVEL_NO_INVOKE != 1 ]]; then
         atfile.say.debug "Invoking '$command'...\n↳ Arguments: ${args[*]}"