python3Packages.protobuf4: pin to protobuf_25

25 is the last version that claims compatibility with protobuf4.
I've removed the comment, as it doesn't seem that later versions will
ever be supported.

pkgs/development/python-modules/protobuf/4.nix

@@ -124,8 +124,6 @@ buildPythonPackage {
     homepage = "https://developers.google.com/protocol-buffers/";
     license = licenses.bsd3;
     maintainers = with maintainers; [ knedlsepp ];
-    # Tests are currently failing because backend is unavailable and causes tests to fail
-    # Progress tracked in https://github.com/NixOS/nixpkgs/pull/264902
     broken = lib.versionAtLeast protobuf.version "26";
   };
 }

pkgs/top-level/python-packages.nix

@@ -10623,7 +10623,7 @@ self: super: with self; {
 
   # Protobuf 4.x
   protobuf4 = callPackage ../development/python-modules/protobuf/4.nix {
-    protobuf = pkgs.protobuf;
+    protobuf = pkgs.protobuf_25;
   };
 
   # Protobuf 5.x