Replace launchpad.net/api with api.launchpad.net @ apt_repository module

This patch is a refactoring change. It replaces one Launchpad endpoint URL with another on a subdomain. There is no functional effect to this whatsoever.

PR #81978

Refs:
* https://github.com/ansible/ansible/pull/81978#issuecomment-1767062178
* https://bugs.launchpad.net/launchpad/+bug/2039251/comments/12

changelogs/fragments/81978-launchpad-api-endpoint.yml

@@ -0,0 +1,3 @@
+---
+minor_changes:
+  - apt_repository.py - use api.launchpad.net endpoint instead of launchpad.net/api

lib/ansible/modules/apt_repository.py

@@ -456,7 +456,9 @@ class SourcesList(object):
 
 class UbuntuSourcesList(SourcesList):
 
-    LP_API = 'https://launchpad.net/api/1.0/~%s/+archive/%s'
+    # prefer api.launchpad.net over launchpad.net/api
+    # see: https://github.com/ansible/ansible/pull/81978#issuecomment-1767062178
+    LP_API = 'https://api.launchpad.net/1.0/~%s/+archive/%s'
 
     def __init__(self, module):
         self.module = module