fish_config: use xdg-open [URL] on Sailfish OS

This is a follow-up to #8811, which fixed fish_config on newer versions of
Sailfish OS.

Using the previous method to open the fish_config URL on Sailfish OS worked
only on 4.4 (and 4.3 IIRC), but not on older OS versions. Opening the URL
using xdg-open works well with new and old OS version, and has been tested on

- Sony Xperia 10 II running SFOS 4.4 aarch64
- Sony Xperia XA2 Ultra running SFOS 4.4 armv7hl
- Sony Xperia X running SFOS 4.1 armv7hl
- Jolla Phone running SFOS 3.4 armv7hl

Closes #8872

share/tools/web_config/webconfig.py

@@ -1696,8 +1696,10 @@ def runThing():
             sys.exit(-1)
     elif is_termux():
         subprocess.call(["termux-open-url", url])
-    elif is_chromeos_garcon() or is_sailfish_os():
+    elif is_chromeos_garcon():
         webbrowser.open(url)
+    elif is_sailfish_os():
+        subprocess.call(["xdg-open", url])
     else:
         webbrowser.open(fileurl)