Use Julia 1.11 for AutoDiff_Ext tests

[albertomercurio]

Description

This PR fixes the CI configuration for the AutoDiff extension tests. Autodiff doesn't work on Julia 1.12, so the test matrix has been updated to run AutoDiff_Ext tests on Julia 1.11 instead of the latest Julia version.

Changes

• Updated .github/workflows/CI.yml to use Julia 1.11 for AutoDiff_Ext tests instead of Julia 1 (latest)

Motivation

This ensures that the AutoDiff extension tests pass until compatibility with Julia 1.12 can be resolved.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.95%. Comparing base (7a2a5fc) to head (cfab210).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #560       +/-   ##
===========================================
+ Coverage   25.20%   92.95%   +67.74%     
===========================================
  Files          51       51               
  Lines        3507     3548       +41     
===========================================
+ Hits          884     3298     +2414     
+ Misses       2623      250     -2373     

☔ 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.