chore: rubocop

see https://github.com/easyPEP/jsonapi.rb/actions/runs/17267231602/job/49002149588?pr=2

```
Running RuboCop...
RuboCop failed!
Inspecting 18 files
................C.

Offenses:

spec/pagination_spec.rb:61:15: C: [Correctable] Rails/CompactBlank: Use compact_blank instead.
            }.reject { |_k, _v| _v.blank? }
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
spec/pagination_spec.rb:160:15: C: [Correctable] Rails/CompactBlank: Use compact_blank instead.
            }.reject { |_k, _v| _v.blank? }
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

18 files inspected, 2 offenses detected, 2 offenses autocorrectable
```

Author: martingregoire

spec/pagination_spec.rb

@@ -53,13 +53,16 @@
 
         context 'on page 2 out of 3' do
           let(:as_list) { }
+          # .compact_blank is not available in our Rails version
+          # rubocop:disable Rails/CompactBlank
           let(:params) do
             {
               page: { number: 2, size: 1 },
               sort: '-created_at',
               as_list: as_list
             }.reject { |_k, _v| _v.blank? }
           end
+          # rubocop:enable Rails/CompactBlank
 
           context 'on an array of resources' do
             let(:as_list) { true }
@@ -153,12 +156,15 @@
 
         context 'on paging beyond the last page' do
           let(:as_list) { }
+          # .compact_blank is not available in our Rails version
+          # rubocop:disable Rails/CompactBlank
           let(:params) do
             {
               page: { number: 5, size: 1 },
               as_list: as_list
             }.reject { |_k, _v| _v.blank? }
           end
+          # rubocop:enable Rails/CompactBlank
 
           context 'on an array of resources' do
             let(:as_list) { true }