infra: Update Poetry version, to current latest (1.8.4) (#28194)

Update all Poetry versions to the current latest, 1.8.4 .

I was checking how lock files are managed and found out that even though
the files are generated - updated with the current latest version of
Poetry, the version used in CI and Dockerfile was outdated.

*
https://github.com/langchain-ai/langchain/pull/28061/files#diff-e00422d37a73d07c174e7838ad7c30f642d06305aff8f9d71e1e84c6897efbffL1
*
https://github.com/langchain-ai/langchain/pull/28070/files#diff-55267c883e58892916d5316bc029725fdeeba5a77e2557cf7667793823d9d9c6L1
*
https://github.com/langchain-ai/langchain/pull/27991/files#diff-9f96b8fd39133c3f1d737e013c9042b065b42ae04b3da76902304f30cec136d8R1

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Co-authored-by: Erick Friis <[email protected]>