sql: fix implicit txn flag in console

Release note (bug fix): Fixed the statement activity page so that it no
longer shows multi-statement implicit transactions as "explicit."

pkg/sql/conn_executor_exec.go

@@ -1117,8 +1117,7 @@ func (ex *connExecutor) dispatchToExecutionEngine(
 
 	// include gist in error reports
 	ctx = withPlanGist(ctx, planner.instrumentation.planGist.String())
-
-	if planner.autoCommit {
+	if planner.extendedEvalCtx.TxnImplicit {
 		planner.curPlan.flags.Set(planFlagImplicitTxn)
 	}