chore(template): fix pull request template

[Antreesy]

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🏚️ Before	🏡 After
Screenshot before	Screenshot after

☀️ Light theme	🌑 Dark Theme

🏁 Checklist

• 🌏 Tested with Chrome, Firefox and Safari or should not be risky to browser differences
  - [ ] 🖥️ Tested with Desktop client or should not be risky for it
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

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