Bugfix: compiler asset type fix

[OscarLuu]

Due to the python2 -> python3 migrations, data uri's need to have the proper typing to be able to reference assets correctly.

Base64 encoding returns bytestrings which then are referenced in data_uri's that look like this:

url(data:image/svg+xml;base64,b'SIgeG1sbnM9Imh0')

>>> encoded = base64.b64encode(open('sample.svg', 'rb').read())
>>> encoded
b'D0iNDAiIGhlaWdodD0iNDAiIHZpZXdCb3g9IjAgMCA0MCA0MCIgZmlsbD0ibm9uZSIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLz'

In order to fix this, we should decode the byte string into string to allow the proper decoding of the data_uri.

>>> encoded = base64.b64encode(open('sample.svg', 'rb').read()).decode('utf-8')
>>> encoded
'D0iNDAiIGhlaWdodD0iNDAiIHZpZXdCb3g9IjAgMCA0MCA0MCIgZmlsbD0ibm9uZSIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLz'

This PR also addresses testing and ensuring github actions testing works properly and as intended

[jehiah]

None is the default value from .get and can be removed.