chg: dev: minor variable name change !minor

bin/compose-core

@@ -1721,9 +1721,9 @@ export -f relation-set
 
 
 _config_merge() {
-    local config_filename="$1" merge_to_file="$2"
+    local config_filename="$1" mixin="$2"
     touch "$config_filename" &&
-    merge_yaml "$config_filename" "$merge_to_file" > "$config_filename.tmp" || return 1
+    merge_yaml "$config_filename" "$mixin" > "$config_filename.tmp" || return 1
     mv "$config_filename.tmp" "$config_filename"
 }
 export -f _config_merge