fix: sd-radio-group aria-describedby not exposing error messages to screen readers (#2985)

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## Description:
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Closes #1648
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- [x] Stories (features, a11y) are created/updated
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Author: balco0110

.changeset/violet-streets-stick.md

@@ -0,0 +1,5 @@
+---
+'@solid-design-system/components': patch
+---
+
+Fixed `sd-radio-group` error messages so they are announced by screen readers.

packages/components/src/components/radio-group/radio-group.ts

@@ -140,6 +140,22 @@ export default class SdRadioGroup extends SolidElement implements SolidFormContr
     this.formControlController.updateValidity();
   }
 
+  updated(changedProperties: Map<string, unknown>) {
+    super.updated(changedProperties);
+    this.syncAriaDescription();
+  }
+
+  // Set aria-description imperatively as a VoiceOver workaround here so static a11y linters do not reject role="radiogroup".
+  private syncAriaDescription() {
+    const fieldset = this.shadowRoot?.querySelector('fieldset');
+    const message = this.showInvalidStyle ? this.validationMessage : '';
+    if (message) {
+      fieldset?.setAttribute('aria-description', message);
+    } else {
+      fieldset?.removeAttribute('aria-description');
+    }
+  }
+
   private getAllRadios() {
     const radios = [...this.querySelectorAll<SdRadio | SdRadioButton>('sd-radio, sd-radio-button')];