python3Packages.aiohttp: fixup package set

In b1d8335904 pytestCheckHook was overridden.
Overriding as is done in this commit breaks cross. Therefore, I attempted
to use one of the spliced sets but that did not work and got accidentally
committed and pushed.

pkgs/top-level/python-packages.nix

@@ -251,7 +251,7 @@ in {
   aiohomekit = callPackage ../development/python-modules/aiohomekit { };
 
   aiohttp = callPackage ../development/python-modules/aiohttp {
-    pytestCheckHook = self.pkgsBuildHost.pytestCheckHook.override { pytest = self.pytest_6_1; };
+    pytestCheckHook = self.pytestCheckHook.override { pytest = self.pytest_6_1; };
   };
 
   aiohttp-cors = callPackage ../development/python-modules/aiohttp-cors { };