Updated Alpine Linux Java to 21

[Xvier]

We use wiremock alpine in our company, but its been flagged because of insecure Java 11 version. With this PR the version will be JRE 21 and remove the java security warnings

References

• TODO

Submitter checklist

• [ x ] Recommended: Join WireMock Slack to get any help in #help-contributing or a project-specific channel like #wiremock-java
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• [ x ] The PR title represents the desired changelog entry
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• Test coverage that demonstrates that the change works as expected
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