Fix: Use seconds for schedule_delay metric when using dogstatsd

[lostkamp]

closes: #18599, #18622

This PR just fixes the failing test from a previos PR: #18622

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[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[ashb]

I'm not sure if we are planning a 2.2.4 (or if we'll go straight to 2.3.0), but if we are I've marked it for inclusion there.