Requiring Maven 3.9 for Quarkus projects?

[gsmet]

I recently created a PR to require Maven 3.9 to build Quarkus-based projects (i.e. not just Quarkus itself but all Quarkus applications).

Maven 3.9 was released on January 2023 so 3 years ago and when we adjust things in our Maven infrastructure, we always have a little voice (a.k.a. @cstamas) telling us that this will work with Maven 3.9 but might work slightly differently with Maven 3.8.

Given we don't actually have tests for Maven 3.8, I think it's time to require Maven 3.9.
Note that we did a previous attempt in June 2024 and it failed because UBI 8 images were still using Maven 3.8.
Back then we decided to be safe and drop the Maven 3.9 requirement for now.

From what I can see, we moved to UBI 9 images quite some time ago and they are using Maven 3.9 so I think we should be safe now.

I want to make sure we all agree it is a good change before doing it. This would be done for 3.31 and so the next LTS.