fix(test-infra): update to jdk21 for fedora:43

[squakez]

JDK17 is missing in the newer container image. For the sake of test it is fine to upgrade to any newer JDK version. Added a note to remind to run integration tests locally when changing the container images versions.

Closes CAMEL-22933

Description

Target

• I checked that the commit is targeting the correct branch (Camel 4 uses the main branch)

Tracking

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Apache Camel coding standards and style

• I checked that each commit in the pull request has a meaningful subject line and body.

• I have run mvn clean install -DskipTests locally from root folder and I have committed all auto-generated changes.

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