Fix formatting of release notes (#18534)

PiperOrigin-RevId: 536324450
Change-Id: I62c0aa7c91f5b38ddae9fae0127ea7b3fb601862

Co-authored-by: Ian (Hee) Cha <heec@google.com>

scripts/release/relnotes.py

@@ -209,11 +209,13 @@ def get_external_authors_between(base, head):
         print("+", note)
       print()
   else:
+    print()
     for note in filtered_relnotes:
       print("+", note)
 
   print()
   print("Acknowledgements:")
   external_authors = get_external_authors_between(merge_base, "HEAD")
+  print()
   print("This release contains contributions from many people at Google" +
         ("." if not external_authors else f", as well as {external_authors}."))