releases/mcap-cli/v0.0.40

mcap convert: Fix duplicate type definition in ROS2 schemas (#1058)

### Public-Facing Changes
FIx `mcap convert` producing ROS2 schemas with duplicate type
definitions

### Description
It could happen that `mcap convert` produced ROS2 schemas with
duplicated subtype definitions if the subtype was included multiple
times by various `.msg` files. This PR fixes this by only processing
subtypes that haven't been processed before.

Resolves FG-6369