feat: add in dotnet 9 fix for codeql build

[wmundev]

https://github.com/twcclegg/libphonenumber-csharp/actions/runs/11840336347/job/32993909242 is failing because no dotnet 9 is available on that github action

Changes

• add in dotnet 9 fix for codeql build

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.27%. Comparing base (7847c6f) to head (14745f5).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #274   +/-   ##
=======================================
  Coverage   75.27%   75.27%           
=======================================
  Files          34       34           
  Lines        4424     4424           
  Branches     1001     1001           
=======================================
  Hits         3330     3330           
  Misses        885      885           
  Partials      209      209           

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