Add Bosnian Cyrillic (ijekavica) date translations

[branislavroljic]

This PR adds Bosnian Cyrillic ijekavian variants to bs-Cyrl via supplementary date translation data.

The existing ekavian forms are left unchanged; ijekavian forms are added as additional valid variants to improve coverage for Bosnian users.

Testing:

• Ran tox locally (pre-commit and docs pass; remaining failures are known Windows-specific issues)
• Manually verified parsing of new phrases using locales=["bs-Cyrl"]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.60%. Comparing base (f0f9102) to head (1204eeb).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1293   +/-   ##
=======================================
  Coverage   96.60%   96.60%           
=======================================
  Files         235      235           
  Lines        2889     2889           
=======================================
  Hits         2791     2791           
  Misses         98       98           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Gallaecio]

Please, run pre-commit run --all-files.