Fix download/all linux32 esr-next 404s

[janbrasna]

One-line summary

Skips ESR–next condition if linux i686, which no longer ships.

Significant changes and points to review

There are generally version constraints for product details, however this ESR branch overlap seems to be bolted on top. There might be more systemic solution somewhere, however once 140esr is over in a few months this while arch code can be removed from all places, so it doesn't have to be pretty or smart for now.

Issue / Bugzilla link

#1726

Testing

http://localhost:8000/en-US/download/all/desktop-esr/linux/af/ (only single ESR, no 404)
http://localhost:8000/en-US/download/all/desktop-esr/linux64-aarch64/af/ (control, 2 ESRs)
http://localhost:8000/en-US/download/all/desktop-esr/win/af/ (control, 3 ESRs)

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.43%. Comparing base (cc4978f) to head (9a2a488).

Files with missing lines	Patch %	Lines
springfield/firefox/views.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1732      +/-   ##
==========================================
- Coverage   88.43%   88.43%   -0.01%     
==========================================
  Files         171      171              
  Lines       12093    12095       +2     
==========================================
+ Hits        10695    10696       +1     
- Misses       1398     1399       +1     

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