fix: change the metal grates on the outside of the level 1 of the convention center to their non-indoor version

[0Monet]

Checklist

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• I wrote the PR title in conventional commit format.
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Purpose of change

Change the metal grates on the outside of the level 1 of the convention center to their non-indoor version, since I hadn't noticed that "!" was used both indoors and outdoors.

Describe the solution

Add "?": "t_grate" to convention_palette and replace the three metal grate tiles outside the convention center level 1 with "t_grate" instead of "t_grate_indoor"

Describe alternatives you've considered

none

Additional context

Before:

After: