Upgrade Caffeine to 3.1.8

[gsmet]

Noticed while working on cache stuff.

[quarkus-bot]

Status for workflow Quarkus CI

This is the status report for running Quarkus CI on commit 3b335c9.

✅ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

You can consult the Develocity build scans.

---

Flaky tests - Develocity

⚙️ JVM Tests - JDK 17

📦 extensions/panache/hibernate-reactive-rest-data-panache/deployment

✖ io.quarkus.hibernate.reactive.rest.data.panache.deployment.repository.PanacheRepositoryResourcePutMethodTest.shouldUpdateComplexObject - History

• 1 expectation failed. JSON path name doesn't match. Expected: is "updated collection" Actual: empty collection - java.lang.AssertionError

java.lang.AssertionError: 
1 expectation failed.
JSON path name doesn't match.
Expected: is "updated collection"
  Actual: empty collection

	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481)

[gsmet]

@DavideD apparently, the test above is a bit flaky. It's not related to this PR as I see it failing from time to time before that.

[gastaldi]

Add to the dependabot.yml as well?