fix: pin cryptography<46 for PyPy 3.10 CI builds (#1860)

Author: WilliamBergamin

requirements/testing.txt

@@ -5,6 +5,8 @@ pytest-asyncio<2  # for async
 pytest-cov>=2,<8
 click==8.0.4  # black is affected by https://github.com/pallets/click/issues/2225
 psutil>=6.0.0,<8
+# cryptography 46+ dropped PyPy 3.10 wheels; pin to <46 for PyPy 3.10 only
+cryptography<46; implementation_name == "pypy" and python_version == "3.10"
 #  used only under slack_sdk/*_store
 boto3<=2
 # For AWS tests