Remove pytest as a requirement to run app (#15449)

* Remove pytest as a requirment to run app

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
(cherry picked from commit 0421d6b)

Author: 2 people

src/lightning_app/testing/helpers.py

@@ -3,7 +3,6 @@
 from queue import Empty
 from typing import List, Optional, Tuple
 
-import pytest
 from packaging.version import Version
 
 from lightning_app import LightningFlow, LightningWork
@@ -64,6 +63,8 @@ def __new__(
         cloud: bool = False,
         **kwargs,
     ):
+        import pytest
+
         """
         Args:
             *args: Any :class:`pytest.mark.skipif` arguments.