Add new release branch to release against rancher action (#5418)

Author: thardeck

.github/workflows/release-against-rancher.yml

@@ -18,6 +18,7 @@ on:
         #   (currently: Fleet minor - 1 = Rancher minor)
         options:
           - main
+          - release/v0.16
           - release/v0.15
           - release/v0.14
           - release/v0.13