Upgrade SixLabors.ImageSharp to 3.1.7

[Moustafaa91]

fixes #1776

• I have read the Contribution Guidelines
• I have commented on the issue above and discussed the intended changes
• A maintainer has signed off on the changes and the issue was assigned to me
• All newly added code is adequately covered by tests
• All existing tests are still running without errors
• The documentation was modified to reflect the changes OR no documentation changes are required.

Changes

• Upgraded SixLabors.ImageSharp package to 3.1.7 due to high-severity vulnerability according to the advisory

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[patriksvensson]

Merged! Thank you for your contribution. Much appreciated! 👍