Fix py parser not treating 204/304/1xx as an empty body

[bdraco]

What do these changes do?

204/304/1xx are now always treated as an empty body in the py parser to match the c parser and comply with https://datatracker.ietf.org/doc/html/rfc9112#section-6.3

Are there changes in behavior for the user?

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
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