Changelog 20.0: Fix broken links

[shlomi-noach]

Description

Somewhat late seeing that we code-freezed, this PR fixes a couple broken links in the 20.0 changelog.

I've also reviewed the PR for spell checking, it looks good.

To be backported to release-20.0 and then to release-20.0-rc

Related Issue(s)

#16010

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Tests were added or are not required
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• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[frouioui]

Good catch!