clientupdate: return OS-specific version from LatestTailscaleVersion (#11812)

We don't always have the same latest version for all platforms (like
with 1.64.2 is only Synology+Windows), so we should use the OS-specific
result from pkgs JSON response instead of the main Version field.

Updates #11795

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

clientupdate/clientupdate.go

@@ -1295,10 +1295,23 @@ func LatestTailscaleVersion(track string) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	if latest.Version == "" {
+	ver := latest.Version
-		return "", fmt.Errorf("no latest version found for %q track", track)
+	switch runtime.GOOS {
+	case "windows":
+		ver = latest.MSIsVersion
+	case "darwin":
+		ver = latest.MacZipsVersion
+	case "linux":
+		ver = latest.TarballsVersion
+		if distro.Get() == distro.Synology {
+			ver = latest.SPKsVersion
+		}
+	}
+
+	if ver == "" {
+		return "", fmt.Errorf("no latest version found for OS %q on %q track", runtime.GOOS, track)
 	}
-	return latest.Version, nil
+	return ver, nil
 }
 
 type trackPackages struct {