python3Packages.pyln-proto: update to nixos 24.05

- coincurve has been bumped to v20 on pyln-proto master without further
  code changes, so using v19 is fine

- the breaking changes in cryptography 42 don't affect pyln-proto
  https://github.com/pyca/cryptography/blob/main/CHANGELOG.rst

pkgs/python-packages/pyln-proto/default.nix

@@ -29,4 +29,10 @@ buildPythonPackage rec {
   checkInputs = [ pytestCheckHook ];
 
   postUnpack = "sourceRoot=$sourceRoot/contrib/pyln-proto";
+
+  postPatch = ''
+    substituteInPlace pyproject.toml \
+      --replace-fail 'coincurve = "^18"' 'coincurve = "^19"' \
+      --replace-fail 'cryptography = "^41"' 'cryptography = "^42"' \
+  '';
 }