Match ::I18n.t call just like I18n.t does

[sato11]

Fixes #751.

Given this model definition;

class Post < ApplicationRecord
  def hello
    I18n.t("hello")
  end

  def world
    ::I18n.t("world")
  end
end

and this dictionary;

en:
  hello: "Hello"
  world: "World"

the unused task used to falsely flag the I18n.t instance with the scope resolution operator (::) prepended.

% i18n-tasks unused
#StandWithUkraine
Unused keys (1) | i18n-tasks v1.1.2
+--------+-------+-------+
| Locale | Key   | Value |
+--------+-------+-------+
|   en   | world | World |
+--------+-------+-------+

This change fixes it, and also adds a test suite that covers #scan_file which directly consumes the enhanced matcher.

Below is how one test case out of two fails without the fix:

Failures:

  1) I18n::Tasks::Scanners::RubyScanner #scan_file when source contains ::I18n.t calls is expected to be present
     Failure/Error: it { is_expected.to be_present }
       expected `[].present?` to be truthy, got false
     # ./spec/ruby_scanner_spec.rb:36:in 'block (4 levels) in <top (required)>'

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2 examples, 1 failure