fix(css): temporary add ?. after this.getModuleInfo in vite:css-post

[sapphi-red]

Description

unocss passes {} as the pluginContext and this.getModuleInfo is undefined in that case.
https://github.com/unocss/unocss/blob/355558bd779997f61aab798b2a1912426064b216/packages-integrations/vite/src/modes/global/build.ts#L183-L187
#19418 added a this.getModuleInfo call and broke unocss.
This is technically a bug in unocss, but since the patch on our side is small and can avoid breakage on their side, I think we can add this ?. for now. Let's remove it in Vite 7.

See https://discord.com/channels/804011606160703521/1342361424370077818/1342395667598938202

[sapphi-red]

/ecosystem-ci run

[pkg-pr-new]

Open in Stackblitz

npm i https://pkg.pr.new/vite@19478

commit: 1d5adf7

[vite-ecosystem-ci]

📝 Ran ecosystem CI on 1d5adf7: Open

suite	result	latest scheduled
astro	❌ failure	❌ failure
histoire	❌ failure	❌ failure
nuxt	✅ success	❌ failure
unocss	✅ success	❌ failure
vike	❌ failure	❌ failure
vitest	✅ success	❌ failure

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