fix(ui5-popover): header valueStateMessage is sized properly

[Vonahz]

Fixes: #13031

[ui5-webcomponents-bot]

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[cla-assistant]

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2 out of 3 committers have signed the CLA.

✅ Vonahz
✅ PetyaMarkovaBogdanova
❌ ui5-webcomponents-bot
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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
2 out of 3 committers have signed the CLA.

✅ PetyaMarkovaBogdanova
✅ Vonahz
❌ ui5-webcomponents-bot
_{You have signed the CLA already but the status is still pending? Let us recheck it.}