[CI] Use Ubuntu 24.04 image, more code coverage, disable CodeQL completely

[gwynne]

• When running Swift 5.10 images, use the Ubuntu 24.04 "Noble Numbat" image.
• Upload code coverage for all Linux test runs, not just 5.10's; Codecov intelligently merges results. This makes coverage numbers more accurate.
• Comment out the CodeQL job altogether rather than just skipping it so it doesn't clutter the Github UI.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.07%. Comparing base (5c26876) to head (8e6e44a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #482      +/-   ##
==========================================
- Coverage   60.12%   55.07%   -5.06%     
==========================================
  Files         125      127       +2     
  Lines        9172    10155     +983     
==========================================
+ Hits         5515     5593      +78     
- Misses       3657     4562     +905     

see 5 files with indirect coverage changes