test(telegram): guard PTB integration tests with importorskip

CI test slices don't install python-telegram-bot (optional dep), causing
a ModuleNotFoundError on collection. Add pytest.importorskip('telegram')
before the PTB imports.

tests/test_telegram_polling_progress_ptb.py

@@ -3,6 +3,8 @@
 import asyncio
 
 import pytest
+
+pytest.importorskip("telegram")  # PTB is an optional dependency; skip if absent.
 from telegram.error import Conflict, TelegramError
 from telegram.request import BaseRequest