knot-resolver-manager_6: fix pname

The pythonMetadataCheckPhase now fails otherwise:
https://hydra.nixos.org/build/338371734/nixlog/3/tail

I should probably figure out a transition on nixpkgs side to different
pnames and attribute names for knot-resolver* packages.

pkgs/by-name/kn/knot-resolver-manager_6/package.nix

@@ -9,7 +9,7 @@ let
 in
 assert lib.versionAtLeast kresd.version "6.0.0";
 python3Packages.buildPythonPackage {
-  pname = "knot-resolver-manager_6";
+  pname = "knot-resolver";
   inherit (kresd) version src;
   pyproject = true;