[24.1] Fix duplicated requests when browsing files sources with pagination

[davelopez]

Partially addresses #18369

An additional unpaginated request was inadvertently triggered when browsing FilesSources which supports pagination.

Thank you @bwalkowi for reporting!

Before

After

How to test the changes?

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  • Follow the steps in Redundant scandir calls when listing source plugin #18369

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

Thank you @davelopez!