[Clang-format] Update clang-format in continuous integrator to use a more recent version (v 18.1.8)

[bodhinandach]

Describe the PR
Clang-format has long been updated to newer versions; the one we used in the Docker was set at v10. Some of the old formatting styles have been deprecated, which causes many repetitive conflicts if one runs with more recent clang-format locally.

This PR updates the default version considered in the continuous integrator (for testing purposes) to v18. It is not the newest version, but compatible with major Linux Ubuntu and macOS distributions used by the group.

Related Issues/PRs
N/A

Additional context
N/A

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.76%. Comparing base (b690d4a) to head (8707c32).
⚠️ Report is 61 commits behind head on master.

Files with missing lines	Patch %	Lines
include/loads_bcs/displacement_constraint.h	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #118      +/-   ##
==========================================
- Coverage   95.76%   95.76%   -0.00%     
==========================================
  Files         244      244              
  Lines       51467    51470       +3     
==========================================
+ Hits        49284    49286       +2     
- Misses       2183     2184       +1     

☔ 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.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[cgeudeker]

Everything looks good to me.