Fix check for other stores in brand store

[steverydz]

Done

Fixed a bug where a store that includes another store will not load

How to QA

• Go to https://snapcraft-io-4315.demos.haus/admin
• Check that all the stores you have access to load

Issue / Card

Fixes #4314

[codecov]

Codecov Report

Merging #4315 (427b897) into main (7b883af) will not change coverage.
The diff coverage is n/a.

❗ Current head 427b897 differs from pull request most recent head c23da1b. Consider uploading reports for the commit c23da1b to get more accurate results

@@           Coverage Diff           @@
##             main    #4315   +/-   ##
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  Coverage   87.56%   87.56%           
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  Files          95       95           
  Lines        6653     6653           
=======================================
  Hits         5826     5826           
  Misses        827      827           

Flag	Coverage Δ
python	87.56% <ø> (ø)

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[Lukewh]

👍 LGTM