[TrivialFix] Add bug reference to releasenote

As per request in [0] adding bug reference to releasenote.

[0] I1a308f486fd7b14a9111a3433284e3c4abf65bd3

Change-Id: I13d04e3c4121b172d22730d19cc8a64dde151225
diff --git a/releasenotes/notes/add-return-value-to-retype-volume-a401aa619aaa2457.yaml b/releasenotes/notes/add-return-value-to-retype-volume-a401aa619aaa2457.yaml
index 4abfe9e..ca42014 100644
--- a/releasenotes/notes/add-return-value-to-retype-volume-a401aa619aaa2457.yaml
+++ b/releasenotes/notes/add-return-value-to-retype-volume-a401aa619aaa2457.yaml
@@ -1,5 +1,7 @@
 ---
 fixes:
-  Add a missing return statement to the retype_volume API in the v2 volumes_client library.
-  This changes the response body from None to an empty dictionary.
+  - |
+    Add a missing return statement to the retype_volume API in the v2
+    volumes_client library: Bug#1703997
 
+    This changes the response body from None to an empty dictionary.