Bump Avro to 0.20 (#1644)

## Which issue does this PR close?

Because of improved error messages:
apache/avro-rs#228. This helps a lot when
working on using the Iceberg Avro reader in PyIceberg. Also, when we
ship the Avro reader with PyIceberg, it will allow users for creating
meaningful issues.

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- Closes #.

## What changes are included in this PR?

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## Are these changes tested?

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Author: Fokko