Format mkdocs search index in place

[echoix]

The python module json.tool can use the same file as input and output, that formats in place.
We can also specify to sort the keys, since mkdocs does not assure the order of the keys. It will result in a smaller diff between page builds.

I also set the no indent flag, so there are newlines, but without extra spaces or tabs. The file is a little smaller (faster to load), and still the same facility for git to diff lines (instead of compact, where the whole file is in one line and needs to be replaced)
See https://docs.python.org/3/library/json.html#cmdoption-json.tool-indent

I was about to include this in my pyproject.toml PR, but it can be here alone first

Proposed Changes

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2. …
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Readiness Checklist

Author/Contributor

• Add entry to the CHANGELOG listing the change and linking to the corresponding issue (if appropriate)
• If documentation is needed for this change, has that been included in this pull request

Reviewing Maintainer

• Label as breaking if this is a large fundamental change
• Label as either automation, bug, documentation, enhancement, infrastructure, or performance

[github-actions]

🦙 MegaLinter status: ⚠️ WARNING

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