Fix `RSpec/DescribedClass` cop missed items (#25309)

spec/lib/feed_manager_spec.rb

@@ -161,7 +161,7 @@ RSpec.describe FeedManager do
         list.accounts << bob
         allow(List).to receive(:where).and_return(list)
         status = Fabricate(:status, text: 'I post a lot', account: bob)
-        expect(FeedManager.instance.filter?(:home, status, alice)).to be true
+        expect(described_class.instance.filter?(:home, status, alice)).to be true
       end
 
       it 'returns true for reblog from followee on exclusive list' do
@@ -171,7 +171,7 @@ RSpec.describe FeedManager do
         allow(List).to receive(:where).and_return(list)
         status = Fabricate(:status, text: 'I post a lot', account: bob)
         reblog = Fabricate(:status, reblog: status, account: jeff)
-        expect(FeedManager.instance.filter?(:home, reblog, alice)).to be true
+        expect(described_class.instance.filter?(:home, reblog, alice)).to be true
       end
 
       it 'returns false for post from followee on non-exclusive list' do
@@ -179,7 +179,7 @@ RSpec.describe FeedManager do
         alice.follow!(bob)
         list.accounts << bob
         status = Fabricate(:status, text: 'I post a lot', account: bob)
-        expect(FeedManager.instance.filter?(:home, status, alice)).to be false
+        expect(described_class.instance.filter?(:home, status, alice)).to be false
       end
 
       it 'returns false for reblog from followee on non-exclusive list' do
@@ -188,7 +188,7 @@ RSpec.describe FeedManager do
         list.accounts << jeff
         status = Fabricate(:status, text: 'I post a lot', account: bob)
         reblog = Fabricate(:status, reblog: status, account: jeff)
-        expect(FeedManager.instance.filter?(:home, reblog, alice)).to be false
+        expect(described_class.instance.filter?(:home, reblog, alice)).to be false
       end
     end