Fix two warnings in devtools_testutils folder

[dargilco]

When I run my tests (Python version 3.14) I keep getting the two warnings below. Fixing them in this PR

============================================================================================ test session starts ============================================================================================
platform win32 -- Python 3.14.0, pytest-9.0.1, pluggy-1.6.0
rootdir: e:\src\sdk-repos\azure-sdk-for-python
configfile: setup.cfg
plugins: anyio-4.11.0, asyncio-1.3.0, cov-7.0.0
asyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
collected 2 items

tests\agents\tools\test_agent_image_generation.py .                                                                                                                                                    [ 50%]
tests\agents\tools\test_agent_image_generation_async.py .                                                                                                                                              [100%]

============================================================================================= warnings summary ==============================================================================================
sdk/ai/azure-ai-projects/tests/agents/tools/test_agent_image_generation.py::TestAgentImageGeneration::test_agent_image_generation
sdk/ai/azure-ai-projects/tests/agents/tools/test_agent_image_generation_async.py::TestAgentImageGenerationAsync::test_agent_image_generation_async
  E:\src\sdk-repos\azure-sdk-for-python-2\eng\tools\azure-sdk-tools\devtools_testutils\envvariable_loader.py:71: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
    _logger.warn(

sdk/ai/azure-ai-projects/tests/agents/tools/test_agent_image_generation.py::TestAgentImageGeneration::test_agent_image_generation
sdk/ai/azure-ai-projects/tests/agents/tools/test_agent_image_generation_async.py::TestAgentImageGenerationAsync::test_agent_image_generation_async
  E:\src\sdk-repos\azure-sdk-for-python-2\eng\tools\azure-sdk-tools\devtools_testutils\preparers.py:148: DeprecationWarning: 'asyncio.iscoroutinefunction' is deprecated and slated for removal in Python 3.16; use inspect.iscoroutinefunction() instead
    if asyncio.iscoroutinefunction(fn):

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
================================================================================= 2 passed, 4 warnings in 71.62s (0:01:11) ==================================================================================

[Copilot]

Pull request overview

This PR addresses two deprecation warnings that appear when running tests with Python 3.14 in the devtools_testutils testing framework.

Key Changes:

• Replaced deprecated asyncio.iscoroutinefunction() with inspect.iscoroutinefunction() to avoid Python 3.16 removal
• Changed deprecated _logger.warn() to the standard _logger.warning() method

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
eng/tools/azure-sdk-tools/devtools_testutils/preparers.py	Added inspect import and replaced asyncio.iscoroutinefunction() with inspect.iscoroutinefunction() for detecting coroutine functions
eng/tools/azure-sdk-tools/devtools_testutils/envvariable_loader.py	Replaced deprecated _logger.warn() with _logger.warning() for logging warning messages

The changes are straightforward, correct, and properly address the deprecation warnings mentioned in the PR description. Both replacements follow Python's recommended migration path and maintain the same functionality.

[scbedd]

❤️

[mccoyp]

Thank you for creating a PR!