Update CI/CD dropping unmaintained gcc compilers

[marcoSanti]

Refreshes the CI compiler test matrix in .github/workflows/ci-tests.yaml, dropping outdated images, fixing a resulting apt update failure, and making the build steps resilient to transient failures outside our control.

• Dropped old GCC compilers gcc:9–gcc:11 from the build matrix (kept gcc:12–gcc:16).
• Re-tagged zhongruoyu/llvm-ports from X.0-trixie/X.1-bullseye to plain X-trixie versions (13–21).
• Added new compilers: clang 22 and clang 23 (zhongruoyu/llvm-ports:22-trixie, zhongruoyu/llvm-ports:23-trixie).
• Added -o Acquire::Check-Valid-Until=false to the apt update step (gfortran install) to work around expired repo metadata on older base images.
• Wrapped the "Install packages" and "Run CMake" steps in nick-fields/retry@v3 (3 attempts, 10s wait between retries; 10min timeout for install, 30min timeout for CMake) so transient package-mirror or build-environment failures don't fail CI outright.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.46%. Comparing base (5a6097d) to head (6430076).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #245      +/-   ##
==========================================
- Coverage   63.46%   60.46%   -3.01%     
==========================================
  Files          79       83       +4     
  Lines        3274     3402     +128     
  Branches     2008     2070      +62     
==========================================
- Hits         2078     2057      -21     
- Misses        399     1061     +662     
+ Partials      797      284     -513     

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