fix: update slot key filtering to exclude internal keys (#2167)

Author: edison1105

Diff for: packages/vue-i18n-core/src/components/Translation.ts

@@ -62,7 +62,7 @@ export const TranslationImpl: ComponentOptions<TranslationProps> =
         }) as unknown as Composer & ComposerInternal)
 
       return (): VNodeChild => {
-        const keys = Object.keys(slots).filter(key => key !== '_')
+        const keys = Object.keys(slots).filter(key => key[0] !== '_')
         const options = create() as TranslateOptions
         if (props.locale) {
           options.locale = props.locale