Fix config section name for humboldt_mesh

[trhille]

Change config section name from humboldt to humboldt_mesh. This was
causing the mesh_gen test case to fail.

[xylar]

Seems to have snuck through testing in #318.

[xylar]

@trhille, as long as you can post something about testing that failed without this and passes with it, it's an obvious fix.

[trhille]

When using master, the Humboldt mesh generation case failed:

(compass_spack_albany) 14:42:52 trhille@ba023 /lustre/scratch4/turquoise/trhille/Humboldt_mesh_20220404_originmaster$compass run
landice/humboldt/mesh_gen
  * step: mesh
      Failed
  test execution:      ERROR
  see: case_outputs/landice_humboldt_mesh_gen.log
  test runtime:        00:09
Test Runtimes:
00:09 FAIL landice_humboldt_mesh_gen
Total runtime 00:09
FAIL: 1 test failed, see above.

case_outputs//landice_humboldt_mesh_gen.log shows that the error is due to an call to a section of the config file called humboldt, which was changed to humboldt_mesh in #318:

Exception raised in run()
Traceback (most recent call last):
  File "/turquoise/usr/projects/climate/trhille/compass/compass/run/serial.py", line 130, in run_tests
    test_case.run()
  File "/turquoise/usr/projects/climate/trhille/compass/compass/testcase.py", line 162, in run
    self._run_step(step, self.new_step_log_file)
  File "/turquoise/usr/projects/climate/trhille/compass/compass/testcase.py", line 278, in _run_step
    step.run()
  File "/turquoise/usr/projects/climate/trhille/compass/compass/landice/tests/humboldt/mesh.py", line 67, in run
    cell_width, x1, y1, geom_points, geom_edges = self.build_cell_width()
  File "/turquoise/usr/projects/climate/trhille/compass/compass/landice/tests/humboldt/mesh.py", line 215, in build_cell_width
    cell_width = set_cell_width(self, section='humboldt', thk=thk,
  File "/turquoise/usr/projects/climate/trhille/compass/compass/landice/mesh.py", line 151, in set_cell_width
    section = self.config[section]
  File "/usr/projects/climate/trhille/miniconda3/envs/compass_spack_albany/lib/python3.9/site-packages/mpas_tools/config.py", line 420, in __getitem__
    return self.combined[section]
  File "/usr/projects/climate/trhille/miniconda3/envs/compass_spack_albany/lib/python3.9/configparser.py", line 963, in __getitem__
    raise KeyError(key)
KeyError: 'humboldt'

After implementing this change:

landice/humboldt/mesh_gen
  * step: mesh
  test execution:      SUCCESS
  test runtime:        03:34
Test Runtimes:
03:34 PASS landice_humboldt_mesh_gen
Total runtime 03:34
PASS: All passed successfully!

[xylar]

Thanks for fixing this, @trhille!