nixpkgs-lint: ignore user's overlays

Otherwise, it can get tripped up importing things like the NUR packages. Since
this is for linting Nixpkgs itself, ignoring overlays seems the way to go.

Changed files
+1 -1
maintainers
scripts
+1 -1
maintainers/scripts/nixpkgs-lint.pl
···
) or exit 1;
# Evaluate Nixpkgs into an XML representation.
-
my $xml = `nix-env -f '$path' -qa '$filter' --xml --meta --drv-path`;
+
my $xml = `nix-env -f '$path' --arg overlays '[]' -qa '$filter' --xml --meta --drv-path`;
die "$0: evaluation of ‘$path’ failed\n" if $? != 0;
my $info = XMLin($xml, KeyAttr => { 'item' => '+attrPath', 'meta' => 'name' }, ForceArray => 1, SuppressEmpty => '' ) or die "cannot parse XML output";