amphetype: conditionally include qtwayland in buildInputs

pkgs/by-name/am/amphetype/package.nix

@@ -1,5 +1,6 @@
 {
   lib,
+  stdenv,
   copyDesktopItems,
   fetchFromGitLab,
   makeDesktopItem,
@@ -28,7 +29,8 @@ python3Packages.buildPythonApplication {
     qt5.wrapQtAppsHook
   ];
 
-  buildInputs = [
+  # qtwayland is a Linux-only Qt platform plugin; it is unsupported on Darwin.
+  buildInputs = lib.optionals stdenv.hostPlatform.isLinux [
     qt5.qtwayland
   ];