Pass file name to Babel transform for better errors

[silvenon]

Before:

SyntaxError: unknown: Expected corresponding JSX closing tag for <br> (12:164)

After:

SyntaxError: /Users/me/my-project/docs/index.mdx: Expected corresponding JSX closing tag for <br> (12:164)

https://babeljs.io/docs/en/options#filename

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[silvenon]

Actually, hold on, I'll add a test.

[silvenon]

Done! I'm not sure what the CI error is about 😕 is it related?

[johno]

Awesome, thank you @silvenon! The CI failure is unrelated.