Passing a -c configuration to rubocop hides the pending cops warnings

[cover]

Expected behavior

When rubocop is called by passing a configuration file (rubocop -c .rubocop.yml) it shows the pending cops warnings like it does when it's called without configuration file (rubocop).

Actual behavior

By passing the configuration file it's not showing any warning. I know it's using the .rubocop file in both cases because it's not showing the frozen string warning.

Steps to reproduce the problem

mkdir rubocop-bug
cd rubocop-bug
echo "source 'https://rubygems.org'\ngem 'rubocop', '0.81'" > Gemfile
echo "def test\n  raise Exception, 'Error message here'\nend" > test.rb
echo "Style/FrozenStringLiteralComment:\n  Enabled: false" > .rubocop.yml
bundle
rubocop
rubocop -c .rubocop.yml

Output

$ rubocop    
The following cops were added to RuboCop, but are not configured. Please set Enabled to either `true` or `false` in your `.rubocop.yml` file:
 - Lint/RaiseException (0.81)
 - Lint/StructNewOverride (0.81)
 - Style/HashEachMethods (0.80)
 - Style/HashTransformKeys (0.80)
 - Style/HashTransformValues (0.80)
For more information: https://docs.rubocop.org/en/latest/versioning/
Inspecting 2 files
..

2 files inspected, no offenses detected

$ rubocop -c .rubocop.yml
Inspecting 2 files
..

2 files inspected, no offenses detected

RuboCop version

0.81.0

Ruby version

2.7.0

[dvandersluis]

@koic you were working on this at one point, want to pick it back up? 😁