buildRustCrate: fixup usage of `builtins.filterSource`

While unifying most of the lib function calls I accidentially changed
the filterSource functions as well. Since there were no tests I ended
up forgetting about this case (even thought I ran into it…).

pkgs/build-support/rust/build-rust-crate/helpers.nix

@@ -11,14 +11,14 @@
      else
        features
    ) [] (lib.attrNames feat);
-  include = includedFiles: src: lib.filterSource (path: type:
+  include = includedFiles: src: builtins.filterSource (path: type:
      lib.any (f:
        let p = toString (src + ("/" + f));
        in
        p == path || (lib.strings.hasPrefix (p + "/") path)
      ) includedFiles
   ) src;
-  exclude = excludedFiles: src: lib.filterSource (path: type:
+  exclude = excludedFiles: src: builtins.filterSource (path: type:
     lib.all (f:
        !lib.strings.hasPrefix (toString (src + ("/" + f))) path
     ) excludedFiles