Provide example CI builds without a container

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The advice here is strongly towards containers (like Earthly), but it is good to show working examples of relying on direct GitHub containers in the CI pipeline when a project does not have a local build that matches CI.

This is both reading & code samples.

Result of this card should be:

• GitHub workflow for Gradle directly without using Earthly
• GitHub workflow for Maven directly without using Earthly

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See @sgammon's fork for an example.

https://github.com/sgammon/modern-java-practices

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Discussion with @jwlibby.