Update dependency @tryghost/release-utils to v0.6.4

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
@tryghost/release-utils	devDependencies	patch	0.6.3 -> 0.6.4

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Release Notes

TryGhost/Ghost-Utils

### [`v0.6.4`](https://togithub.com/TryGhost/Ghost-Utils/compare/@tryghost/release-utils@0.6.3...@tryghost/release-utils@0.6.4) [Compare Source](https://togithub.com/TryGhost/Ghost-Utils/compare/@tryghost/release-utils@0.6.3...@tryghost/release-utils@0.6.4)

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