Accept pending cops in the development build

Follow up of rubocop#7646 (comment).

This PR accepts pending cops in the development build.

Some tests fail with the following warnings when using the
`Enabled: pending` status.

```console
% bundle exec rake spec
(snip)

1) RuboCop::CLI --only when one cop is given accepts cop names from
plugins
     Failure/Error: raise output

     RuntimeError:
       The following cops were added to RuboCop, but are not
configured. Please set Enabled to either `true` or `false` in your
`.rubocop.yml` file:
        - Style/ZeroLengthPredicate
       Inspecting 2 files
       ..

       2 files inspected, no offenses detected
     # ./spec/rubocop/cli/cli_options_spec.rb:213:in `block (4 levels)
in <top (required)>'
     # ./spec/support/cli_spec_behavior.rb:26:in `block (2 levels) in
<top (required)>'
     # ./lib/rubocop/rspec/shared_contexts.rb:29:in `block (4 levels) in
<top (required)>'
     # ./lib/rubocop/path_util.rb:67:in `chdir'
     # ./lib/rubocop/path_util.rb:67:in `chdir'
     # ./lib/rubocop/rspec/shared_contexts.rb:28:in `block (3 levels) in
<top (required)>'
     # ./lib/rubocop/rspec/shared_contexts.rb:8:in `block (2 levels) in
<top (required)>'
```

This PR prevents those tests from catching a pending cop warning.
OTOH, this PR supplements the E2E test for a pending cop warning.

spec/rubocop/cli/cli_options_spec.rb

@@ -207,9 +207,47 @@ class SomeCop < Cop
         # process. Otherwise, the extra cop will affect other specs.
         output =
           `ruby -I . "#{rubocop}" --require redirect.rb --only Style/SomeCop`
-        expect($CHILD_STATUS.success?).to be_truthy
+        # Excludes a warning when new `Enabled: pending` status cop is specified
+        # in config/default.yml.
+        output_excluding_warn_for_pending_cops =
+          output.split("\n").last(4).join("\n") << "\n"
+        expect(output_excluding_warn_for_pending_cops)
+          .to eq(<<~RESULT)
+            Inspecting 2 files
+            ..
+
+            2 files inspected, no offenses detected
+          RESULT
+      end
+
+      it 'accepts cop names from plugins with a pending cop' do
+        create_file('.rubocop.yml', <<~YAML)
+          require: rubocop_ext
+
+          Style/SomeCop:
+            Description: Something
+            Enabled: pending
+        YAML
+        create_file('rubocop_ext.rb', <<~RUBY)
+          module RuboCop
+            module Cop
+              module Style
+                class SomeCop < Cop
+                end
+              end
+            end
+          end
+        RUBY
+        create_file('redirect.rb', '$stderr = STDOUT')
+        rubocop = "#{RuboCop::ConfigLoader::RUBOCOP_HOME}/exe/rubocop"
+        # Since we define a new cop class, we have to do this in a separate
+        # process. Otherwise, the extra cop will affect other specs.
+        output =
+          `ruby -I . "#{rubocop}" --require redirect.rb --only Style/SomeCop`
         expect(output)
           .to eq(<<~RESULT)
+            The following cops were added to RuboCop, but are not configured. Please set Enabled to either `true` or `false` in your `.rubocop.yml` file:
+             - Style/SomeCop
             Inspecting 2 files
             ..
 

spec/support/suppress_pending_warning.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+#
+# This is a file that supports testing. An open class has been applied to
+# `RuboCop::ConfigLoader.warn_on_pending_cops` to suppress pending cop
+# warnings during testing.
+#
+module RuboCop
+  class ConfigLoader
+    class << self
+      def warn_on_pending_cops(config)
+        # noop
+      end
+    end
+  end
+end