Fix test-related issues (#17888)

* Remove obsolete RSS::Serializer test

Since #17828, RSS::Serializer no longer has specific code for deleted statuses,
but it is never called on deleted statuses anyway.

* Rename erroneously-named test files

* Fix failing test

* Fix test deprecation warnings

* Update CircleCI Ruby orb

1.4.0 has a bug that does not match all the test files due to incorrect
globbing

spec/controllers/admin/accounts_controller_spec.rb

@@ -194,9 +194,7 @@ RSpec.describe Admin::AccountsController, type: :controller do
   end
 
   describe 'POST #unblock_email' do
-    subject do
-      -> { post :unblock_email, params: { id: account.id } }
-    end
+    subject { post :unblock_email, params: { id: account.id } }
 
     let(:current_user) { Fabricate(:user, admin: admin) }
     let(:account) { Fabricate(:account, suspended: true) }
@@ -206,11 +204,11 @@ RSpec.describe Admin::AccountsController, type: :controller do
       let(:admin) { true }
 
       it 'succeeds in removing email blocks' do
-        is_expected.to change { CanonicalEmailBlock.where(reference_account: account).count }.from(1).to(0)
+        expect { subject }.to change { CanonicalEmailBlock.where(reference_account: account).count }.from(1).to(0)
       end
 
       it 'redirects to admin account path' do
-        subject.call
+        subject
         expect(response).to redirect_to admin_account_path(account.id)
       end
     end
@@ -219,7 +217,7 @@ RSpec.describe Admin::AccountsController, type: :controller do
       let(:admin) { false }
 
       it 'fails to remove avatar' do
-        subject.call
+        subject
         expect(response).to have_http_status :forbidden
       end
     end