fix(god): fix cursor color

[darth10]

This was broken in aa079b0 (#7049).

When the cursor changes from color A to color B, it doesn't ever change back to color A, as (face 'cursor) will now return color B.
Since the default cursor in the Doom theme uses the highlight background color, we can use that when setting the cursor color when this module is enabled.

Screenshots

For example, when the :editor god module is enabled, change the cursor color by moving to the end of a long line, and then move to the beginning of the line so that the default cursor color should be shown.

Before

After

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