Exit pre mode (#714)

* Exit pre mode

* Remove prerelease-only changesets

.changeset/pre/all-cars-grin.md

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-"@changesets/action": patch
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-
-Fix the computed publish plan path passed internally to `changeset pack` by the `/pack` subaction.

.changeset/pre/green-birds-push.md

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-"@changesets/action": patch
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-
-Fixed a regression making it impossible to sync new versions of versioning pull requests with base branch updates when using GitHub API pushes.

.changeset/pre/quick-spoons-smile.md

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-"@changesets/action": patch
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-Fix support for prerelease exits using the new `.changeset/pre` layout.

.changeset/pre/ready-mangos-boil.md

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-"@changesets/action": patch
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-Fixed usage of `--from-publish-plan` flag used by the `/pack` subaction

.changeset/pre/silent-tips-dance.md

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-"@changesets/action": patch
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-Fix the `/version` subaction to not crash on missing `pr-base-branch` input. This input is meant to be optional.