clientupdate: do not allow msiexec to reboot the OS (#11409)

According to
https://learn.microsoft.com/en-us/windows/win32/msi/standard-installer-command-line-options#promptrestart,
`/promptrestart` is ignored with `/quiet` is set, so msiexec.exe can
sometimes silently trigger a reboot. The best we can do to reduce
unexpected disruption is to just prevent restarts, until the user
chooses to do it. Restarts aren't normally needed for Tailscale updates,
but there seem to be some situations where it's triggered.

Updates #18254

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

clientupdate/clientupdate.go

@@ -836,7 +836,7 @@ func (up *Updater) switchOutputToFile() (io.Closer, error) {
 func (up *Updater) installMSI(msi string) error {
 	var err error
 	for tries := 0; tries < 2; tries++ {
-		cmd := exec.Command("msiexec.exe", "/i", filepath.Base(msi), "/quiet", "/promptrestart", "/qn")
+		cmd := exec.Command("msiexec.exe", "/i", filepath.Base(msi), "/quiet", "/norestart", "/qn")
 		cmd.Dir = filepath.Dir(msi)
 		cmd.Stdout = up.Stdout
 		cmd.Stderr = up.Stderr