nuttx/boards:fix kconfig under apps/testing folder that change config-testing-mm to config-testing-heap

[txy-21]

Summary

Under apps/testing folder, the macro of CONFIG_TESTING_MM is changed to CONFIG_TESTING_HEAP.
So we need to update the defconfig containing CONFIG_TESTING_HEAP in the nuttx/boards folder.

Impact

folder impact : nuttx/boards

Testing

CI TEST.

[nuttxpr]

[Experimental Bot, please feedback here]

No, this PR does not fully meet the NuttX requirements. While it addresses some aspects, it's missing crucial information. Here's a breakdown:

• Insufficient Summary: While it mentions the code change (CONFIG_TESTING_MM to CONFIG_TESTING_HEAP), it lacks the why. Why was this macro name change necessary? What problem does it solve? What functionality does it affect? This is the most important part of the summary.

• Missing Impact Details: Simply stating "folder impact: nuttx/boards" is insufficient. Which boards are affected? How are they affected? Will users of these boards need to change their configurations? Will any board functionality change? Provide specifics.

• Inadequate Testing Information: "CI TEST" is not enough. Which CI tests were run? What were the specific results? The requirement asks for "Testing logs before change" and "Testing logs after change". Just stating "CI TEST" provides no evidence of actual verification. What host and target configurations were used for testing?

• Missing Other Impact Assessments: The PR description completely omits assessments of impact on users, build process, hardware, documentation, security, and compatibility. Even if the answer to some of these is "NO", explicitly stating so is required.

In short: The PR needs to be significantly more detailed to meet the NuttX requirements. Provide the missing why, elaborate on the impacts (even if they are "NO"), and include actual testing logs/results with specific host and target information.