Replace env.deprecated_call() with pytest.deprecated_call()

Since we already require pytest>=6 (see tests/requirements.txt), the
old compatibility function is obsolete and pytest.deprecated_call() can
be used directly.

Extracted from PR pybind#5879

Co-authored-by: Michael Carlstrom <rmc@carlstrom.com>
Co-authored-by: gentlegiantJGC <gentlegiantJGC@users.noreply.github.com>

Author: 3 people

tests/test_builtin_casters.py

@@ -304,7 +304,7 @@ def cant_convert(v):
     # TODO: Avoid DeprecationWarning in `PyLong_AsLong` (and similar)
     # TODO: PyPy 3.8 does not behave like CPython 3.8 here yet (7.3.7)
     if sys.version_info < (3, 10) and env.CPYTHON:
-        with env.deprecated_call():
+        with pytest.deprecated_call():
             assert convert(Int()) == 42
     else:
         assert convert(Int()) == 42
@@ -377,7 +377,7 @@ def require_implicit(v):
     # TODO: PyPy 3.8 does not behave like CPython 3.8 here yet (7.3.7)
     # https://github.com/pybind/pybind11/issues/3408
     if (3, 8) <= sys.version_info < (3, 10) and env.CPYTHON:
-        with env.deprecated_call():
+        with pytest.deprecated_call():
             assert convert(np.float32(3.14159)) == 3
     else:
         assert convert(np.float32(3.14159)) == 3