chore: restore next npm tag for prerelease versions

[Copilot]

Recent workflow changes broke the npm dist-tag for prerelease versions. Versions like 3.5.4-beta.0 were being published under the beta tag instead of the original next tag.

Changes

• .github/workflows/test-and-release.yaml: Updated automatic publish step to use next tag
• .github/workflows/publish-to-npm.yaml: Changed tag option and conditional from beta to next
• RELEASE.md: Updated documentation to reflect next tag usage

Context

The version suffix (-beta.X) remains unchanged—only the npm dist-tag is corrected. Users install prerelease versions via:

npm install apify@next

Previous behavior (incorrect):

• Version 3.5.4-beta.0 → beta tag

Restored behavior:

• Version 3.5.4-beta.0 → next tag

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Publish prerelease versions to npm under next tag.</issue_title>
<issue_description>Recent changes to the publishing workflow changed this - the prerelease versions are now published under beta tag, which is not consistent with the original behaviour (which used next tag).

</issue_description>

<agent_instructions>make minimal changes while fixing this. only comment very hard to understand sections of code. the PR title should follow semantic commits (chore: etc.)</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Publish prerelease versions to npm under next tag. #557

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