WebM not a valid image file extension

[Former user]

Initial migration fails because WebM is not recognized as a valid image file extension. WebM is the recommend format for animated assets for Foundry (https://foundryvtt.com/article/media/#:~:text=For%20transparent%20video%20assets%2C%20such%20as%20animated%20tiles%20or%20tokens%2C%20.webm%20will%20generally%20provide%20the%20best%20experience%20as%20it%20is%20high%20quality%20with%20a%20small%20file%20size.). Not able to use in a world that has animated tokens.

[Kim Mantas]

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