add miniflare v5 changelog

[emily-shen]

changelog for miniflare v5

dated to the next workers-sdk release which should have the first non-alpha release

[cloudflare-docs-bot]

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This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/changelog/	@cloudflare/pm-changelogs, @cloudflare/product-owners

[github-actions]

Preview URL: https://a8c6889f.preview.developers.cloudflare.com
Preview Branch URL: https://codex-miniflare-v5-alpha-changelog.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/changelog/post/2026-09-08-miniflare-v5/	https://codex-miniflare-v5-alpha-changelog.preview.developers.cloudflare.com/changelog/post/2026-09-08-miniflare-v5/