Update importer 'contents' invalid type tests to bogus object rather …

[Goodwine]

…than a Buffer

The Buffer seems to be replaced as a string correctly in dart-sass-embedded, making these tests fail for the wrong reason. Instead of failing for the wrong type it was failing for invalid Sass.

See - #1834

[Goodwine]

NVM it seems like dart-sass-embedded just renders it like a toString() 🤔

[ntkme]

For embedded-host-node, it only sets a string on protobuf messages:

• Whether a type can be converted to string or not is actually done via protobuf, therefore the printed error message is not the same.
• When a type can be converted to string, protobuf will implicitly convert it as string, and then for URL it will be checked on the dart side, thus again producing a different error message.

Finally there is an issue where if an object is implicitly converted to a string sourceMapUrl, and the sourceMapUrl is not absolute, the dart side do thrown an error but span is missing.

[Goodwine]

I see where to make the fixes now, I will revert this PR and reopen another with updated tests in a bit