python3Packages.radios: relax pycountry version constraint

pycountry was updated from 24.6.1 to 26.2.16 (#491301), but radios
pins pycountry to ^24.0.0 (i.e. <25). The only pycountry API radios
uses is countries.get(alpha_2=...), which is unchanged in v26.

Upstream has an open PR to bump the constraint (frenck/python-radios#1483)
but no release yet.

Use pythonRelaxDepsHook to drop the upper bound until upstream releases.

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

@@ -35,6 +35,8 @@ buildPythonPackage rec {
       --replace-fail 'version = "0.0.0"' 'version = "${version}"'
   '';
 
+  pythonRelaxDeps = [ "pycountry" ];
+
   build-system = [
     poetry-core
   ];