librewolf-bin: mark with knownVulnerabilities due to lack of maintenance in nixpkgs

This security-critical package is currently not maintained well enough
to be kept as is.
We are currently providing a 4 months old version which is not
acceptable for a browser. PR #464467 created by r-ryantm 3 weeks ago was
not handled by anyone.

See also #416711 for previous discussions.

pkgs/by-name/li/librewolf-bin-unwrapped/package.nix

@@ -113,5 +113,8 @@ stdenv.mkDerivation {
     mainProgram = "librewolf";
     hydraPlatforms = [ ];
     sourceProvenance = with lib.sourceTypes; [ binaryNativeCode ];
+    knownVulnerabilities = [
+      "librewolf-bin lacks maintenance in nixpkgs, consider using an alternative"
+    ];
   };
 }