[jk] Update backfill policy to allow update on settings

[johnson-mage]

Description

• Fix backfill policy error when updating "Max concurrent runs" setting for backfill.

How Has This Been Tested?

Confirmed the error below no longer appears when saving backfill with "Max concurrent runs" input filled:

Checklist

• The PR is tagged with proper labels (bug, enhancement, feature, documentation)
• I have performed a self-review of my own code
• I have added unit tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• If new documentation has been added, relative paths have been added to the appropriate section of docs/mint.json