qt6.qtdeclarative: fix code-signing on Darwin

The build tries to sign qmltestrunner, but sometimes it’s already
signed, causing the signing to fail due to an existing signature.
Cherry-pick this patch from upstream to force sign it regardless.

pkgs/development/libraries/qt-6/modules/qtdeclarative/default.nix

@@ -10,6 +10,7 @@
   lib,
   pkgsBuildBuild,
   replaceVars,
+  fetchpatch2,
 }:
 
 qtModule {
@@ -28,16 +29,24 @@ qtModule {
     darwin.sigtool
   ];
 
-  patches = [
-    # invalidates qml caches created from nix applications at different
-    # store paths and disallows saving caches of bare qml files in the store.
-    (replaceVars ./invalidate-caches-from-mismatched-store-paths.patch {
-      nixStore = builtins.storeDir;
-      nixStoreLength = builtins.toString ((builtins.stringLength builtins.storeDir) + 1); # trailing /
-    })
-    # add version specific QML import path
-    ./use-versioned-import-path.patch
-  ];
+  patches =
+    [
+      # invalidates qml caches created from nix applications at different
+      # store paths and disallows saving caches of bare qml files in the store.
+      (replaceVars ./invalidate-caches-from-mismatched-store-paths.patch {
+        nixStore = builtins.storeDir;
+        nixStoreLength = builtins.toString ((builtins.stringLength builtins.storeDir) + 1); # trailing /
+      })
+      # add version specific QML import path
+      ./use-versioned-import-path.patch
+    ]
+    ++ lib.optionals stdenv.hostPlatform.isDarwin [
+      # The build attempts to sign qmltestrunner, which may already be signed, causing it to fail unless forced.
+      (fetchpatch2 {
+        url = "https://invent.kde.org/qt/qt/qtdeclarative/-/commit/8effbbcefd8cae27cd5da07b4ffe3aa86dad83bf.diff";
+        hash = "sha256-wKrKXdr1ddshpRVIZZ/dsn87wjPXSaoUvXT9edlPtzA=";
+      })
+    ];
 
   preConfigure =
     let