workflows: merge multiple Windows uploads together

[patrick-stephens]

Resolves failure in CI: https://github.com/fluent/fluent-bit/actions/runs/7260326110/job/19779963759

Previous to PR #8304 we were using v3 version of the action which allowed us to add all Windows binaries into the same package. Now we have separate packages so have to merge them together to properly sync to S3.

Taken from https://github.com/actions/download-artifact/tree/v4/?tab=readme-ov-file#download-multiple-filtered-artifacts-to-the-same-directory.

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