Update protobuf in dev-requirements.txt

[srprash]

Addresses https://github.com/aws-observability/aws-otel-python-instrumentation/security/dependabot/30

Description of changes:

• Version picked to what we use in other places: https://github.com/aws-observability/aws-otel-python-instrumentation/blob/main/contract-tests/images/mock-collector/pyproject.toml#L16

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