Increase sleep time in end-to-end test to wait for relaying unreceived packets

[soareschen]

Closes: #1216

Description

This increases the sleep time from 10 seconds to 20 seconds, which hopefully provides enough time for the relayer to relay all packets during the CI end-to-end tests.

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For contributor use:

• Updated the Unreleased section of CHANGELOG.md with the issue.
• If applicable: Unit tests written, added test to CI.
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments.
• Re-reviewed Files changed in the Github PR explorer.

[romac]

Thanks! I will re-run the job a few times and then if the error does not pop up again we can merge it.