component/avahi: Add libexpat.

Avahi was not buildable on Debian 11.
10 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed Cloudooo.UnitTest-Master

00:07:05

passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

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failed ERP5.StandaloneDeploymentScriptTest-Debian.Buster.Master

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passed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Buster

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passed SlapOS.Eggs.UnitTest-Master.Python2

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passed SlapOS.Eggs.UnitTest-Master.Python3

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failed SlapOS.SoftwareReleases.IntegrationTest-Master

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failed SlapOS.Theia.ResilienceTest-Master-ERP5

01:46:37

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

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failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

15:02:11