Pushing text files result in a wrong mime type error

[gaelgatelement]

Describe the bug

Using the following curl command :

curl -k -H 'Host: synapse.dev.local' -X POST --header 'Authorization: Bearer {user_access_token}' --header 'Content-Type: text/plain' --data-binary <text file> 'https://localhost/_matrix/media/v3/upload

When getting the file, Matrix content scanner returns the following error :

2023-09-27 16:21:04,922 - matrix_content_scanner.scanner.scanner - 518 - ERROR - GET-1348 - Mismatching MIME type (text/plain) and Content-Type header (text/plain; charset=UTF-8)

[reivilibre]

Synapse appends UTF-8 charsets

    # Default to a UTF-8 charset for text content types.
    # ex, uses UTF-8 for 'text/css' but not 'text/css; charset=UTF-16'
    if media_type.lower() in TEXT_CONTENT_TYPES:
        content_type = media_type + "; charset=UTF-8"
    else:
        content_type = media_type

We need to only compare the 'essence' of the MIME type.