GitHub workflow simple-build.yaml should cache dependencies

[fabiobrz]

SSIA, to speed up CI checks, and reduce network traffic.

See https://docs.github.com/en/actions/use-cases-and-examples/building-and-testing/building-and-testing-java-with-maven#caching-dependencies

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• Environment: GitHub workflows, automated CI checks
• Steps to reproduce: e.g. create, or push changes to, a PR to see that the GitHub workflow based simple-build CI checks always download all the Maven dependencies