Fixes exception thrown when pickling/unpickling ProductAttributesContainer

[crgwbr]

After #4167 and prior to this patch, trying to use pickle with a Product or ProductAttributesContainer results in a recursion error.

[codecov]

Codecov Report

Merging #4271 (204b9a7) into master (cb93f5e) will increase coverage by 0.44%.
Report is 11 commits behind head on master.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4271      +/-   ##
==========================================
+ Coverage   87.84%   88.28%   +0.44%     
==========================================
  Files         291      293       +2     
  Lines       16145    16046      -99     
==========================================
- Hits        14182    14166      -16     
+ Misses       1963     1880      -83     

Files	Coverage Δ
src/oscar/apps/catalogue/product_attributes.py	98.13% <100.00%> (+0.08%)	⬆️

... and 10 files with indirect coverage changes

[crgwbr]

@specialunderwear The test failure here seems unrelated to my change, and a very similar issue seems to be occurring in master¹. Any ideas on why?

Footnotes

1. https://github.com/django-oscar/django-oscar/actions/runs/8510200510/job/23307293806 ↩

[specialunderwear]

@specialunderwear The test failure here seems unrelated to my change, and a very similar issue seems to be occurring in master1. Any ideas on why?

Footnotes

1. https://github.com/django-oscar/django-oscar/actions/runs/8510200510/job/23307293806 ↩

Yeas we have some ideas and we're working on it, but we can't reproduce this locally unfortunately, can you?

[crgwbr]

Yeas we have some ideas and we're working on it, but we can't reproduce this locally unfortunately, can you?

Unfortunately, no. The tests all pass for me locally.