opentelemetry-instrumentation-aiohttp-client: fix tests for real

Author: xrmx

Diff for: instrumentation/opentelemetry-instrumentation-aiohttp-client/tests/test_aiohttp_client_integration.py

@@ -886,7 +886,9 @@ def response_hook(
 
 class TestLoadingAioHttpInstrumentor(unittest.TestCase):
     def test_loading_instrumentor(self):
-        eps = entry_points("opentelemetry_instrumentor", "aiohttp-client")
+        (entry_point,) = entry_points(
+            group="opentelemetry_instrumentor", name="aiohttp-client"
+        )
 
-        instrumentor = next(eps).load()()
+        instrumentor = entry_point.load()()
         self.assertIsInstance(instrumentor, AioHttpClientInstrumentor)