fix(NcTimeZonePicker): scope css styles

[Antreesy]

☑️ Resolves

• Fix leaking styles to all NcSelects

Not sure, if left rule should be applied, see it's broken on master, but at least scoped to timezone:

Current	Expected

🖼️ Screenshots

<template>
	<span>
		<NcDateTimePicker
			v-model="time"
			type="datetime"
			:show-timezone-select="true"
			:timezone-id.sync="tz" /><br>
		{{ time }} | {{ tz }}
		<br>
		<NcSelect v-model="tz"/>
	</span>
</template>

🏚️ Before	🏡 After

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 3️⃣ Backport to next requested with a Vue 3 upgrade

[ShGKme]

Thanks

[Antreesy]

/backport to next