update-third-party: read attributes from the worktree

This should be done so that any attributes for ignoring certain files
when exporting can be appended to the file during the extraction step,
but ignored in the actual import. Necessary for importing the gitsetup
repository.

Utilities/Scripts/update-third-party.bash

@@ -48,7 +48,7 @@
 # Utility functions
 ########################################################################
 git_archive () {
-    git archive --prefix="$name-reduced/" HEAD -- $paths | \
+    git archive --worktree-attributes --prefix="$name-reduced/" HEAD -- $paths | \
         tar -C "$extractdir" -x
 }