add version 26.5.18 migration

[calvin-codecov]

Followup migration for #921

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Note

Low Risk
Low risk: adds a simple data migration that updates a single Constants row; main risk is deploying with an incorrect/undesired version string.

Overview
Adds a new Django migration 0085_increment_version that updates the core.Constants record with key="version" to 26.5.18, chaining after 0084_increment_version.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[codspeed-hq]

Merging this PR will not alter performance

✅ 9 untouched benchmarks

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_{Comparing release/26.5.18-migration (754eb25) with main (9164119)¹}

Footnotes

1. No successful run was found on main (54ba68b) during the generation of this report, so 9164119 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[sentry]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.90%. Comparing base (e5be426) to head (754eb25).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #922   +/-   ##
=======================================
  Coverage   91.90%   91.90%           
=======================================
  Files        1316     1317    +1     
  Lines       50654    50663    +9     
  Branches     1625     1625           
=======================================
+ Hits        46552    46561    +9     
  Misses       3796     3796           
  Partials      306      306           

Flag	Coverage Δ
apiunit	94.95% <ø> (ø)
sharedintegration	36.94% <0.00%> (-0.03%)	⬇️
sharedunit	84.91% <100.00%> (+<0.01%)	⬆️
workerintegration	58.53% <ø> (ø)
workerunit	90.37% <ø> (ø)

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