Parent #13629

This PR updates FluxC to that 'develop' version where ActivityLogStore.ACTIVITY_LOG_PAGE_SIZE is 100 (from previous 20). This step is required in order in order to avoid some of the scrolling issues on the 'Backups' screen due to the fact that the API enhancement is not ready yet.

To test:

• Launch app and go to My Site tab.
• Click on the Activity log menu item to launch the Activity Log screen.
• Scroll to the bottom and verify that the pagination works as expected and that this time the page size is larger (100, from previous 20).
• Go back and click on the Backup menu item to launch the Backup screen.
• Again, scroll to the bottom and verify that the pagination works as expected and that this time the page size is larger (100, from previous 20).
• If you previously encountered an issue with the Backup screen where there were no more items to load, due to the fact that the there were only a couple of rewindable items, thus not filling the available screen estate, verify that this problem is now gone or at least that it became less relevant.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.