Replace deprecated getOrComputeIfAbsent() API calls

[BACtaki]

Replace deprecated getOrComputeIfAbsent() API calls for org.junit.jupiter.api.extension with computeIfAbsent().

Checklist

• 🛡️ Don't disclose security issues! (contact security@apache.org)
• 🔗 Clearly explained why the changes are needed, or linked related issues: Fixes #
• 🧪 Added/updated tests with good coverage, or manually tested (and explained how)
• 💡 Added comments for complex logic
• 🧾 Updated CHANGELOG.md (if needed)
• 📚 Updated documentation in site/content/in-dev/unreleased (if needed)

[BACtaki]

Requesting a quick review @adam-christian-software @snazy @dimas-b

[dimas-b]

As I mentioned in other conversations, this change forced downstream projects that use integration-tests to adopt JUnit 6 (previously only JUnit 5 was required).... so I advised for delaying this change.

However, I can see that there's constant interest from the community to fix these deprecations... so I guess we might as well merge this change and address any (unlikely) fallout as it comes.

I think it might be worth specifically mentioning JUnit 6 in the CHANGELOG, though (section Changes). WDYT?

[BACtaki]

that use integration-tests

You make a very good point @dimas-b . We have to make this change at some point so we might as well make it now IMO. I have added a note in the changelog to highlight the point about downstream projects using JUnit 6. Let's see how it goes- I promise to address any fallout from this change, as unlikely as that may be (:

[adutra]

We have to make this change at some point so we might as well make it now

Wouldn't it be prudent to wait until after the 1.4.0 release, due in the next few days?

[BACtaki]

We have to make this change at some point so we might as well make it now

Wouldn't it be prudent to wait until after the 1.4.0 release, due in the next few days?

We can wait until the 1.4.0 release, there's no rush. Any specific changes in the release you think might be relevant to this PR @adutra ?

[dimas-b]

Yes, merging this after 1.4.0 is branched sounds like a good compromise to me.

[dimas-b]

For reference: the integration-tests module was specifically added for reuse in downstream projects in #590