go/types: propagate *ast.LabeledStmt in blockBranches properly

go/types: propagate *ast.LabeledStmt in blockBranches properly

Fixes #70974

Change-Id: I330c0ae53dcbcdb173ab514ee94f2ca53944df09
GitHub-Last-Rev: 7c2b740da6d6e94ac8787f04ad8942f3776ac56c
GitHub-Pull-Request: golang/go#70976
Reviewed-on: https://go-review.googlesource.com/c/go/+/638257
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Alan Donovan <adonovan@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>