set an error on the test run when we lose DTX connectivity

in most coses this is due to the test runner crashing (or it can also be closed
manually through the UI)

ios/testmanagerd/testlistener.go

@@ -255,6 +255,11 @@ func (t *TestListener) TestRunnerKilled() {
 	t.executionFinished()
 }
 
+func (t *TestListener) FinishWithError(err error) {
+	t.err = err
+	t.executionFinished()
+}
+
 func (t *TestListener) Done() <-chan struct{} {
 	return t.finished
 }

ios/testmanagerd/xcuitestrunner.go

@@ -2,6 +2,7 @@ package testmanagerd
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"path"
@@ -398,12 +399,14 @@ func runXUITestWithBundleIdsXcode15Ctx(
 		if conn1.Err() != dtx.ErrConnectionClosed {
 			log.WithError(conn1.Err()).Error("conn1 closed unexpectedly")
 		}
+		testListener.FinishWithError(errors.New("lost connection to testmanagerd. the test-runner may have been killed"))
 		break
 	case <-conn2.Closed():
 		log.Debug("conn2 closed")
 		if conn2.Err() != dtx.ErrConnectionClosed {
 			log.WithError(conn2.Err()).Error("conn2 closed unexpectedly")
 		}
+		testListener.FinishWithError(errors.New("lost connection to testmanagerd. the test-runner may have been killed"))
 		break
 	case <-testListener.Done():
 		break