IDLE: Fix docs URL in the About window (GH-28417)

(cherry picked from commit 0f17a754)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/idlelib/help_about.py

@@ -91,8 +91,9 @@ def create_widgets(self):
         email = Label(frame_background, text='email:  idle-dev@python.org',
                       justify=LEFT, fg=self.fg, bg=self.bg)
         email.grid(row=6, column=0, columnspan=2, sticky=W, padx=10, pady=0)
-        docs = Label(frame_background, text="https://docs.python.org/"
-                     f"{version[:version.rindex('.')]}/library/idle.html",
+        docs_url = ("https://docs.python.org/%d.%d/library/idle.html" %
+                    sys.version_info[:2])
+        docs = Label(frame_background, text=docs_url,
                      justify=LEFT, fg=self.fg, bg=self.bg)
         docs.grid(row=7, column=0, columnspan=2, sticky=W, padx=10, pady=0)
         docs.bind("<Button-1>", lambda event: webbrowser.open(docs['text']))