Add shorter version of channel_flow test

[nglaser3]

Summary of changes

This PR adds a shorter, non-heavy, version of the channel_flow test. The run time of this shorter version is approximately 20 seconds. This is desired as some of the components being tested in this file were only being tested in heavy tests, causing test failures to slip under the radar.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Required for Merging

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
  • CI tests pass
  • Local tests pass (including Serpent2 integration tests)

Associated Developers

• Dev: @smpark7

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[smpark7]

I wonder if we can avoid creating a new input file by using the original channel-flow.i file and adding cli_args = "Executioner/num_steps=5" in the tests file. I'm not sure whether exodiff takes issue with having an input file for two exodiff tests.