Add option for creating a third-body species in the MICM configuration

[boulderdaze]

Allow users to specify that a species should be treated as a "third-body" species whose concentration is automatically set to the total air density (mol m-3).

Closes musica issue #115

• Updated github action to version 4
• Removed invalid code that sets third body name when it matches M. Setting third body type is done by parser.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.21%. Comparing base (555be4e) to head (787fad0). Report is 9 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #551 +/- ## ========================================== - Coverage 92.25% 92.21% -0.04% ========================================== Files 45 45 Lines 3407 3403 -4 ========================================== - Hits 3143 3138 -5 - Misses 264 265 +1 ```

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