test: fix dead assert in retry streaming tests causing coverage issues (#17723)

## Problem
In `test_retry_streaming.py` and `test_retry_streaming_async.py`, an
assert statement was indented inside the `pytest.raises` context manager
block. In Python testing with `pytest`, any code in a pytest.raises
block that follows line that raises the expected exception is NOT
executed.

This meant that the assert statement intended to verify the exception
message was dead code and never ran.

## Solution
The assert statement has been dedented (moved outside and after the
`pytest.raises` block) to ensure it executes after the exception is
caught. This allows the test to actually verify the exception message as
originally intended.

## Notes to Reviewers
This fix ensures that the tests are actually checking that the exception
contains the message "can't send non-None value". It also helps with
code coverage metrics by removing dead code.

Author: chalmerlowe

packages/google-api-core/tests/asyncio/retry/test_retry_streaming_async.py

@@ -293,7 +293,7 @@ async def test___call___generator_send_retry(self, sleep):
         generator = await retry_(self._generator_mock)(error_on=3)
         with pytest.raises(TypeError) as exc_info:
             await generator.asend("cannot send to fresh generator")
-            assert exc_info.match("can't send non-None value")
+        assert exc_info.match("can't send non-None value")
         await generator.aclose()
 
         # error thrown on 3

packages/google-api-core/tests/unit/retry/test_retry_streaming.py

@@ -263,7 +263,7 @@ def test___call___with_generator_send_retry(self, sleep):
         with pytest.raises(TypeError) as exc_info:
             # calling first send with non-None input should raise a TypeError
             result.send("can not send to fresh generator")
-            assert exc_info.match("can't send non-None value")
+        assert exc_info.match("can't send non-None value")
         # initiate iteration with None
         result = retry_(self._generator_mock)(error_on=3)
         assert result.send(None) == 0