fix(manifest): do not override existing js manifest entry

[dominikg]

from other chunks that share the original filename

see https://discord.com/channels/804011606160703521/1310891839389433986/1310916075352887328

cc @sapphi-red

refs #14945 (comment)

Description

[dominikg]

/ecosystem-ci run

[dominikg]

sveltekit will still fail here as some adaptions of its test-suite are still pending to land on main, but i am going to run a separate flow with that and post the result here

[vite-ecosystem-ci]

📝 Ran ecosystem CI on cd47bd1: Open

suite	result	latest scheduled
analogjs	❌ failure	✅ success
astro	❌ failure	❌ failure
histoire	❌ failure	❌ failure
ladle	❌ failure	✅ success
laravel	❌ failure	✅ success
marko	❌ failure	✅ success
nuxt	❌ failure	✅ success
previewjs	❌ failure	✅ success
quasar	❌ failure	✅ success
qwik	❌ failure	✅ success
rakkas	❌ failure	✅ success
redwoodjs	❌ failure	❌ failure
remix	❌ failure	❌ failure
storybook	❌ failure	✅ success
sveltekit	❌ failure	❌ failure
unocss	❌ failure	✅ success
vike	❌ failure	❌ failure
vite-environment-examples	❌ failure	✅ success
vite-plugin-pwa	❌ failure	✅ success
vite-plugin-react	❌ failure	✅ success
vite-plugin-react-swc	❌ failure	✅ success
vite-plugin-svelte	❌ failure	✅ success
vite-plugin-vue	❌ failure	✅ success
vite-setup-catalogue	❌ failure	✅ success
vitepress	❌ failure	✅ success
vitest	❌ failure	✅ success
vuepress	❌ failure	✅ success
waku	❌ failure	❌ failure

✅

[vite-ecosystem-ci]

📝 Ran ecosystem CI on c7b3308: Open

suite	result	latest scheduled
sveltekit	❌ failure	❌ failure

✅