fix(form-core): prevent choice input from changing name away from parent

packages/form-core/src/choice-group/ChoiceInputMixin.js

@@ -110,6 +110,17 @@ const ChoiceInputMixinImplementation = superclass =>
       if (changedProperties.has('modelValue')) {
         this.__syncCheckedToInputElement();
       }
+
+      if (
+        changedProperties.has('name') &&
+        // @ts-expect-error not all choice inputs have a parent form group, since this mixin does not have a strict contract with the registration system
+        this.__parentFormGroup &&
+        // @ts-expect-error
+        this.__parentFormGroup.name !== this.name
+      ) {
+        // @ts-expect-error not all choice inputs have a name prop, because this mixin does not have a strict contract with form control mixin
+        this.name = changedProperties.get('name');
+      }
     }
 
     constructor() {

packages/form-core/test-suites/choice-group/ChoiceGroupMixin.suite.js

@@ -112,6 +112,23 @@ export function runChoiceGroupMixinSuite({ parentTagString, childTagString } = {
       expect(el.formElements[1].name).to.equal('gender2');
     });
 
+    it('prevents updating the name property of a child if it is different from its parent', async () => {
+      const el = /** @type {ChoiceGroup} */ (await fixture(html`
+        <${parentTag} name="gender">
+          <${childTag}></${childTag}>
+          <${childTag}></${childTag}>
+        </${parentTag}>
+      `));
+
+      expect(el.formElements[0].name).to.equal('gender');
+      expect(el.formElements[1].name).to.equal('gender');
+
+      el.formElements[0].name = 'gender2';
+
+      await el.formElements[0].updateComplete;
+      expect(el.formElements[0].name).to.equal('gender');
+    });
+
     it('adjusts the name of a child element if it has a different name than the group', async () => {
       const el = /** @type {ChoiceGroup} */ (await fixture(html`
         <${parentTag} name="gender">