Updates conditions for the 8.0 branch

[nastasha-solomon]

This PR makes two changes to our Mergify config file:

• Moves the entry for 8.0 above 7.17 so it's in the correct order
• Updates the conditions for the 8.0 branch so that the only criteria that need to be met are: PR is merged and the v8.0.0 version label exists

[github-actions]

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[bmorelli25]

LGTM