[8.9](backport #2815) [Fleet] Fix docker publish step in buildkite

[mergify]

This is an automatic backport of pull request #2815 done by Mergify.
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On branch mergify/bp/8.9/pr-2815
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	both modified:   .buildkite/pipeline.yml

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[elasticmachine]

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• Start Time: 2023-07-26T08:50:48.679+0000

• Duration: 40 min 53 sec

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Test	Results
Failed	0
Passed	742
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Total	743

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[jlind23]

buildkite test this

[jlind23]

Buildkite is not mandatory for 8.9 branch hence merging.