Reduce repetition in "dmh allocated" test with macro

[kazarmy]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository.
• I made sure to follow the project's coding style.
• I've documented every RZ_API function and struct this PR changes.
• I've added tests that prove my changes are effective (required for changes to RZ_API).
• I've updated the Rizin book with the relevant information (if needed).

Detailed description

This pr just reduces repetition in the "dmh allocated" test (part of the dbg_dmh testfile) using a macro.

Test plan

All builds are green.

Closing issues

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