Fix failing spec due to deprecation warning

silence should return yield. Added new method capture_output to better describe capturing the output.

```
 DEPRECATION WARNING: config.active_support.remove_deprecated_time_with_zone_name is deprecated and will be removed in Rails 7.2. (called from block (2 levels) in <top (required)> at /home/runner/work/flipper/flipper/spec/flipper/engine_spec.rb:32)
 ```

spec/flipper/adapters/strict_spec.rb

@@ -29,13 +29,13 @@
 
  context "#get" do
  it "raises an error for unknown feature" do
- expect(silence { subject.get(feature) }).to match(/Could not find feature "unknown"/)
+ expect(capture_output { subject.get(feature) }).to match(/Could not find feature "unknown"/)
  end
  end
 
  context "#get_multi" do
  it "raises an error for unknown feature" do
- expect(silence { subject.get_multi([feature]) }).to match(/Could not find feature "unknown"/)
+ expect(capture_output { subject.get_multi([feature]) }).to match(/Could not find feature "unknown"/)
  end
  end
  end

spec/flipper/engine_spec.rb

@@ -29,7 +29,7 @@
 
  let(:config) { application.config.flipper }
 
- subject { application.initialize! }
+ subject { SpecHelpers.silence { application.initialize! } }
 
  shared_examples 'config.strict' do
  let(:adapter) { Flipper.adapter.adapter }

spec/flipper/middleware/memoizer_spec.rb

@@ -285,7 +285,7 @@
  end
 
  def get(uri, params = {}, env = {}, &block)
- silence { super(uri, params, env, &block) }
+ capture_output { super(uri, params, env, &block) }
  end
 
  include_examples 'flipper middleware'

spec/support/spec_helpers.rb

@@ -79,11 +79,22 @@ def silence
  original_stdout = $stdout
 
  # Redirect stderr and stdout
- output = $stderr = $stdout = StringIO.new
+ $stderr = $stdout = StringIO.new
+
+ yield
+ ensure
+ $stderr = original_stderr
+ $stdout = original_stdout
+ end
+
+ def capture_output
+ original_stderr = $stderr
+ original_stdout = $stdout
+
+ output = $stdout = $stderr = StringIO.new
 
  yield
 
- # Return output
  output.string
  ensure
  $stderr = original_stderr