[ci] Fix release process

[Drarig29]

What and why?

Without this explicit permission (as described here), the create-draft-release job fails with:

(403) Resource not accessible by integration

How?

Add an explicit permission for the GITHUB_TOKEN

Review checklist

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration)

[datadog-datadog-prod-us1[bot]]

Datadog Report

Branch report: corentin.girard/fix-release-process Commit report: 2b89aaf Test service: datadog-ci-tests

:white_check_mark: 0 Failed, 392 Passed, 0 Skipped, 1m 28.78s Total duration (2m 4.3s time saved)