homepage-dashboard: fix enableLocalIcons = true build

Fix this build error:

Running phase: installPhase
cp: cannot create regular file '/nix/store/pyxl74qanpdplcjqs7r4g2ywlnaa56ms-homepage-dashboard-1.3.2/share/homepage/public/icons/assetgrid.png': Permission denied

While at it, use "cp -r" instead of globs to prevent potential issues
with overlong command lines.

pkgs/by-name/ho/homepage-dashboard/package.nix

···
 
   installLocalIcons = ''
     mkdir -p $out/share/homepage/public/icons
-    cp ${dashboardIcons}/png/* $out/share/homepage/public/icons
-    cp ${dashboardIcons}/svg/* $out/share/homepage/public/icons
+    cp -r --no-preserve=mode ${dashboardIcons}/png/. $out/share/homepage/public/icons
+    cp -r --no-preserve=mode ${dashboardIcons}/svg/. $out/share/homepage/public/icons
     cp ${dashboardIcons}/LICENSE $out/share/homepage/public/icons/
   '';
 in