beets: mkPlugin: change default testPaths to fit unstable beets as well

pkgs/tools/audio/beets/common.nix

@@ -36,7 +36,21 @@
 let
   inherit (lib) attrNames attrValues concatMap;
 
-  mkPlugin = { name, enable ? !disableAllPlugins, builtin ? false, propagatedBuildInputs ? [ ], testPaths ? [ "test/test_${name}.py" ], wrapperBins ? [ ] }: {
+  mkPlugin = { name
+  , enable ? !disableAllPlugins
+  , builtin ? false
+  , propagatedBuildInputs ? [ ]
+  , testPaths ? [
+    # NOTE: This conditional can be removed when beets-stable is updated and
+    # the default plugins test path is changed
+    (if (lib.versions.majorMinor version) == "1.6" then
+      "test/test_${name}.py"
+    else
+      "test/plugins/test_${name}.py"
+    )
+  ]
+  , wrapperBins ? [ ]
+  }: {
     inherit name enable builtin propagatedBuildInputs testPaths wrapperBins;
   };