Bump eventmachine-tail gem to version 0.6.6

What does this MR do?

Backports this fix to 18.5.

Bump eventmachine-tail gem to version 0.6.6

- Updates the eventmachine-tail gem to version 0.6.6 which both
  clarifies the license and makes changes to enable Ruby 3 support.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/501048

Changelog: changed

Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

Related issues

Related gitlab#501048

Original Merge Request: Bump eventmachine-tail gem to version 0.6.6 (!8735 - merged) • Robert Marshall • 18.6

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