Save Repository Size Limit Set in Admin Group Page Correctly

What does this MR do and why?

This fixes #2116 (closed).

The issue also exists when creating a group via the admin area and setting a repository size limit there. This MR also fixes the issue for group creation.

Screenshots or screen recordings

Before

Screen_Recording_2022-08-24_at_5.46.52_PM

After

Screen_Recording_2022-08-24_at_5.47.50_PM

MR acceptance checklist

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