python3.pkgs.beetcamp: move beets dependency to nativeBuildInputs

This will make it possible to use `beetcamp` without setting
`dontUsePythonCatchConflicts = true` in an override.

See: https://github.com/NixOS/nixpkgs/pull/471166#discussion_r2642534939

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

@@ -40,12 +40,15 @@ buildPythonPackage {
   ];
 
   dependencies = [
-    beets
     httpx
     packaging
     pycountry
   ];
 
+  nativeBuildInputs = [
+    beets
+  ];
+
   nativeCheckInputs = [
     writableTmpDirAsHomeHook
     pytestCheckHook