Reduce concurrency while downloading aggregate

[Neylix]

Description

Decrease the concurrency while downloading the summary aggregate in self repair.
As they are processed one by one, there is no need to download more than 2 in a row

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules