bpo-44059: Register the SerenityOS Browser in the webbrowser module (GH-25947) (GH-25950)

(cherry picked from commit 329a47f0524e9d3f43f1e28c4f9e7c088662c030)

Co-authored-by: Linus Groh <mail@linusgroh.de>
diff --git a/Lib/webbrowser.py b/Lib/webbrowser.py
index 6023c1e..e980497 100755
--- a/Lib/webbrowser.py
+++ b/Lib/webbrowser.py
@@ -532,6 +532,10 @@ def register_standard_browsers():
         # OS X can use below Unix support (but we prefer using the OS X
         # specific stuff)
 
+    if sys.platform == "serenityos":
+        # SerenityOS webbrowser, simply called "Browser".
+        register("Browser", None, BackgroundBrowser("Browser"))
+
     if sys.platform[:3] == "win":
         # First try to use the default Windows browser
         register("windows-default", WindowsDefault)