fix: [compose-core] improve protection of relation data file !minor

Fixes a timing issue where the data in the relation file could be read.

bin/compose-core

@@ -3069,9 +3069,11 @@ get_relation_data_file() {
         new=true
     fi
 
-    if [ "$new" ]; then
+    if [ -n "$new" ]; then
+        OLDUMASK=$(umask)
+        umask 0077
         e "$relation_config" > "$relation_data_file"
-        chmod go-rwx "$relation_data_file"  ## protecting this file
+        umask "$OLDUMASK"
         e "$relation_config" | md5_compat > "$relation_data_file.md5_ref"
     fi
     echo "$relation_data_file"