tstest/natlab: ignore transport errors during gokrazy update (#21441)

In my testing using TCG, I hit non-EOF network errors that made
this test fail. Since we already poll and check the image version
later, we can treat this response as best-effort.

Resolves #21440

Change-Id: Ia923fc2c199aae7a543d00e06d25a375512daa01
Signed-off-by: Francois Marier <francois@tailscale.com>

tstest/natlab/vmtest/gokrazy_update_test.go

@@ -8,7 +8,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"io"
+	"net/url"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -52,8 +52,9 @@ func TestGokrazyUpdatesItselfToSameImage(t *testing.T) {
 		"--unsigned",
 	)
 	if err != nil {
-		if errors.Is(err, io.EOF) {
-			t.Logf("update command connection ended during reboot: %v", err)
+		if urlError, ok := errors.AsType[*url.Error](err); ok {
+			// Ignore transport errors
+			t.Logf("update command connection lost during reboot: %v", urlError)
 		} else {
 			t.Fatalf("gokrazy update command failed: %v\n%s", err, out)
 		}