test(planning_validator): add planning interface test for planning_validator

[kyoichi-sugahara]

Description

The following pull request needs to be merged to this branch:
#3364

Related links

Tests performed

please run the following command and verify that it produces the expected output:

colcon test --event-handlers console_cohesion+ --packages-select planning_validator

If the following output is returned, then the changes in this pull request have passed all tests:

100% tests passed, 0 tests failed out of 5

Notes for reviewers

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