fix: use correct python command name in test_stdio.py

Some platforms (e.g. Fedora) don't provide an unversioned `python`
binary. In such case `tests/client/test_stdio.py` fails when it tries to
call it. Use `sys.executable` instead, which works reliably.

Signed-off-by: Ondrej Mosnáček <omosnacek@gmail.com>

Author: WOnder93

tests/client/test_stdio.py

@@ -69,7 +69,7 @@ async def test_stdio_client():
 @pytest.mark.anyio
 async def test_stdio_client_bad_path():
     """Check that the connection doesn't hang if process errors."""
-    server_params = StdioServerParameters(command="python", args=["-c", "non-existent-file.py"])
+    server_params = StdioServerParameters(command=sys.executable, args=["-c", "non-existent-file.py"])
     async with stdio_client(server_params) as (read_stream, write_stream):
         async with ClientSession(read_stream, write_stream) as session:
             # The session should raise an error when the connection closes