fix: set write permission for PR in ecosystem-ci-trigger workflow

[dominikg]

mistakenly used read before as i thought reactions were enough, but a test showed a 403 so lets try with write...

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[dominikg]

/ecosystem-ci run

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16337

[dominikg]

see https://github.com/vitejs/vite/blob/main/.github/workflows/ecosystem-ci-trigger.yml

it didn't work here, so maybe the rest api only checks against the main branch and we have to merge this first.