Update astro version to 1.0.0-rc.0

[natemoo-re]

Changes

• Updates astro version to 1.0.0-rc.0
• Required before [ci] release #3972

Testing

N/A

Docs

N/A

[changeset-bot]

⚠️ No Changeset found

Latest commit: 481b446

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[FredKSchott]

LGTM!

For anyone following along: This is safe to merge now since we have frozen our automated release bot and are releasing next--rc through a manual snapshot release process that wipes away this version tag regardless of what it is.

With this change, once we unfreeze our automatic CI releases through the changeset bot, that first automatic release will become our first official RC release.