gh-135953: Avoid BytesWarning when sampling profiler tests fail (GH-141719)

With `-bb`, this failed on BytesWarning: str() on a bytes instance

Lib/test/test_profiling/test_sampling_profiler/helpers.py

@@ -83,7 +83,7 @@ def test_subprocess(script):
         response = client_socket.recv(1024)
         if response != b"ready":
             raise RuntimeError(
-                f"Unexpected response from subprocess: {response}"
+                f"Unexpected response from subprocess: {response!r}"
             )
 
         yield SubprocessInfo(proc, client_socket)