fix(mp): ignore value check when stringify style (#3456)

packages/uni-mp-vue/src/helpers/style.ts

-import { isString } from '@vue/shared'
-import { normalizeStyle, stringifyStyle as stringify } from '@vue/shared'
+import { hyphenate, isString, NormalizedStyle } from '@vue/shared'
+import { normalizeStyle } from '@vue/shared'
 export function stringifyStyle(value: unknown) {
   if (isString(value)) {
     return value
   }
   return stringify(normalizeStyle(value))
 }
+
+function stringify(styles: NormalizedStyle | string | undefined): string {
+  let ret = ''
+  if (!styles || isString(styles)) {
+    return ret
+  }
+  for (const key in styles) {
+    ret += `${key.startsWith(`--`) ? key : hyphenate(key)}:${styles[key]};`
+  }
+  return ret
+}