fix: [compose-core] make ``get_relation_data_dir()`` output correct directory even when run from a relation

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

bin/compose-core

@@ -2812,8 +2812,11 @@ get_relation_data_dir() {
         cat "$cache_file"
         return 0
     fi
-
-    project=$(get_default_project_name) || return 1
+    local project relation_dir
+    project=${PROJECT_NAME}
+    if [ -z "$project" ]; then
+        project=$(get_default_project_name) || return 1
+    fi
     relation_dir="$VARDIR/relations/$project/${service}-${target_service}/$relation_name"
     if ! [ -d "$relation_dir" ]; then
         mkdir -p "$relation_dir" || return 1