update VS insertion target to rel/d16.4 (#7770)

Author: brettfo

azure-pipelines.yml

@@ -340,6 +340,6 @@ stages:
   - template: eng/release/insert-into-vs.yml
     parameters:
       componentBranchName: refs/heads/release/dev16.4
-      insertTargetBranch: master
+      insertTargetBranch: rel/d16.4
       insertTeamEmail: fsharpteam@microsoft.com
       insertTeamName: 'F#'