Unshadow allow_untrusted option for pkg artifact

The pkg stanza has an option called `allow_untrusted`, which is
supposed to cause `/usr/sbin/installer` to be called with the
`-allowUntrusted` switch.

PR #3141 seems to have renamed the `pkg_install_opts` field to
`options`. At the same time, it introduces an `options` parameter for
the `run_installer` method, which shadows the `options` getter
method, causing the `allow_untrusted` option to be silently ignored.

The issue affects just the `pkg` stanza because `Hbc::Artifact::Pkg`
is the only artifact class that has an `options` method.

This commit removes the shadowing by renaming the field to
`stanza_options`; in one case, it uses `_options` for a parameter
name (instead of the more canonical `_`) for the sake of clarity.

Library/Homebrew/cask/lib/hbc/artifact/pkg.rb

@@ -9,17 +9,19 @@ module Hbc
     class Pkg < AbstractArtifact
       attr_reader :pkg_relative_path
 
-      def self.from_args(cask, path, **options)
-        options.extend(HashValidator).assert_valid_keys(:allow_untrusted, :choices)
-        new(cask, path, **options)
+      def self.from_args(cask, path, **stanza_options)
+        stanza_options.extend(HashValidator).assert_valid_keys(
+          :allow_untrusted, :choices
+        )
+        new(cask, path, **stanza_options)
       end
 
-      attr_reader :path, :options
+      attr_reader :path, :stanza_options
 
-      def initialize(cask, path, **options)
+      def initialize(cask, path, **stanza_options)
         super(cask)
         @path = cask.staged_path.join(path)
-        @options = options
+        @stanza_options = stanza_options
       end
 
       def summarize
@@ -32,7 +34,7 @@ module Hbc
 
       private
 
-      def run_installer(command: nil, verbose: false, **options)
+      def run_installer(command: nil, verbose: false, **_options)
         ohai "Running installer for #{cask}; your password may be necessary."
         ohai "Package installers may write to any location; options such as --appdir are ignored."
         unless path.exist?
@@ -43,7 +45,9 @@ module Hbc
           "-target", "/"
         ]
         args << "-verboseR" if verbose
-        args << "-allowUntrusted" if options.fetch(:allow_untrusted, false)
+        if stanza_options.fetch(:allow_untrusted, false)
+          args << "-allowUntrusted"
+        end
         with_choices_file do |choices_path|
           args << "-applyChoiceChangesXML" << choices_path if choices_path
           command.run!("/usr/sbin/installer", sudo: true, args: args, print_stdout: true)
@@ -51,7 +55,7 @@ module Hbc
       end
 
       def with_choices_file
-        choices = options.fetch(:choices, {})
+        choices = stanza_options.fetch(:choices, {})
         return yield nil if choices.empty?
 
         Tempfile.open(["choices", ".xml"]) do |file|