python3Packages.respx: run tests in legacy asyncio-mode

Since pytest-asyncio==0.19.0 the strict mode has become the default. The
respx module has not been upgraded with that in mind, so let's rollback
that change to fix the tests.

pkgs/development/python-modules/respx/default.nix

@@ -35,6 +35,10 @@ buildPythonPackage rec {
     trio
   ];
 
+  pytestFlagsArray = [
+    "--asyncio-mode=legacy"
+  ];
+
   postPatch = ''
     sed -i "/--cov/d" setup.cfg
   '';