fix(ui5-carousel): remove redundant role="region" from section element

[kskondov]

The <section> element already has an implicit ARIA role of "region", making the explicit attribute unnecessary and flagged by validators.
Fixes: #11515

[ui5-webcomponents-bot]

🚀 Deployed on https://pr-13561--ui5-webcomponents-preview.netlify.app

[duygu-rmdn]

ariaLabelTxt can return undefined when users don't provide accessibleName or accessibleNameRef (both are optional properties). i am not so sure but i think that this breaks landmark navigation for screen readers. Maybe as a possible fix try this one:

get ariaLabelTxt() {
      return getEffectiveAriaLabelText(this) ||
             Carousel.i18nBundle.getText(CAROUSEL_DEFAULT_LABEL);
  }

[sap-ui5-webcomponents-release]

🎉 This PR is included in version v2.25.0 🎉

The release is available on v2.25.0

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