Update Rust crate rdkafka to 0.38.0

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This PR contains the following updates:

Package	Type	Update	Change
rdkafka	dependencies	minor	0.37.0 -> 0.38.0

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Release Notes

fede1024/rust-rdkafka (rdkafka)

v0.38.0

• Update BaseProducer::poll to not return early, and instead continue
  looping until the passed timeout is reached.
• Breaking change. Change signature for OwnedDeliveryResult. The
  Ok variant is now a Delivery struct, rather than a tuple. This allows
  or including Timestamp as a result field. It means that adding values
  in the future will not require a breaking change.
• Update BaseProducer::flush to correctly call poll internally, until
  all messages have been processed.
• Upgrade all library dependencies.
• Add tests for Kafka versions up to 0.38.0.
• Require a minimum of CMake 3.5 compatibility for CMake build (#​766)

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Configuration

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Branch automerge failure

This PR was configured for branch automerge. However, this is not possible, so it has been raised as a PR instead.

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• Branch has one or more failed status checks

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⚠️ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

♻ Renovate will retry this branch, including artifacts, only when one of the following happens:

• any of the package files in this branch needs updating, or
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The artifact failure details are included below:

File name: Cargo.lock

Command failed: cargo update --config net.git-fetch-with-cli=true --manifest-path risotto/Cargo.toml --package [email protected] --precise 0.38.0
error: failed to acquire package cache lock

Caused by:
  failed to open: /home/ubuntu/.cargo/.package-cache

Caused by:
  failed to create directory `/home/ubuntu/.cargo`

Caused by:
  File exists (os error 17)