Use coverage exclusion comment marker

Author: ncoghlan

httpx/__init__.py

@@ -104,7 +104,7 @@ def main() -> None:  # type: ignore
     if not __name.startswith("__"):
         try:
             setattr(__locals[__name], "__module__", "httpx")  # noqa
-        except AttributeError:  # noqa
+        except AttributeError:  # pragma: no cover
             # typing.Union instances are immutable in Python 3.14+,
             # so don't fail if writing to "__module__" fails
-            continue  # noqa
+            continue  # pragma: no cover