Fix matrix computation for Ubuntu 24

[gsmet]

@holly-cummins I was able to reproduce your issue and this should fix it.

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[gsmet]

Let's merge it and see how it goes as this thing is not really tested by this CI run.

[gsmet]

@holly-cummins if you can rebase your PR, I would be interested to know the result.

[holly-cummins]

@holly-cummins if you can rebase your PR, I would be interested to know the result.

Confirmed that it's working, and I have JVM tests: /~https://github.com/holly-cummins/quarkus/actions/runs/12398637710

(Don't be confused by the confusing name of the last commit in that CI run. I've also forced some of my native and JVM runners onto ubuntu-22 while waiting for #45160, hence the commit about forcing ubuntu 22. The main matrix calculation is running on 24.)

[gsmet]

Awesome, thanks for confirming!