fix(types/computed): ensure type safety for WritableComputedRef

[jh-leong]

close #11576

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	98.7 kB	37.4 kB	33.7 kB
vue.global.prod.js	156 kB	57.2 kB	50.8 kB

Usages

Name	Size	Gzip	Brotli
createApp	54.1 kB	21 kB	19.1 kB
createSSRApp	58.1 kB	22.6 kB	20.6 kB
defineCustomElement	58.8 kB	22.5 kB	20.5 kB
overall	67.7 kB	26 kB	23.7 kB

[jh-leong]

/ecosystem-ci run

[vue-bot]

📝 Ran ecosystem CI: Open

suite	result	latest scheduled
language-tools	❌ failure	❌ failure
nuxt	❌ failure	❌ failure
pinia	✅ success	✅ success
primevue	✅ success	✅ success
quasar	✅ success	✅ success
radix-vue	✅ success	✅ success
router	✅ success	✅ success
test-utils	✅ success	✅ success
vant	❌ failure	❌ failure
vite-plugin-vue	❌ failure	✅ success
vitepress	❌ failure	❌ failure
vue-i18n	❌ failure	❌ failure
vue-macros	❌ failure	❌ failure
vuetify	✅ success	✅ success
vueuse	✅ success	✅ success
vue-simple-compiler	✅ success	✅ success