ci: include pull request id in changelog link (#38504)

Signed-off-by: little-meow-meow <204685920+little-meow-meow@users.noreply.github.com>

Tools/actions_changelogs_since_last_run.py

@@ -189,7 +189,8 @@ def changelog_entries_to_message_lines(entries: Iterable[ChangelogEntry]) -> lis
                     message = message[: DISCORD_SPLIT_LIMIT - 100].rstrip() + " [...]"
 
                 if url is not None:
-                    line = f"{emoji} - {message} [PR]({url}) \n"
+                    pr_number = url.split("/")[-1]
+                    line = f"{emoji} - {message} ([#{pr_number}]({url}))\n"
                 else:
                     line = f"{emoji} - {message}\n"