How to solve "Additional properties are not allowed" error in ROS Noetic Snap creation?

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I am trying to build a ROS Noetic snap and am getting this error:

Failed to load plugin: properties failed to load for control-system: Additional properties are not allowed ('rosinstall-files' was unexpected)

The .yaml file used for this is:

name: robot_control
base: core20
version: '0.1'
summary: ROS package.
description: |
  This is my ROS package.

grade: devel
confinement: devmode

parts:
  control-system:
    plugin: catkin
    source: .
    rosinstall-files: [my_package_snap.rosinstall]
    catkin-packages: [my_package]

apps:
  robot_control:
    command: roslaunch my_package robot_control.launch    
    plugs: [network, network-bind]

The .rosinstall file used is:

- git: {local-name: my_package, uri: 'https://github.com/user/my_package.git', version: master}

Could anyone provide any guidance to overcome this?