[issue45644] Make json.tool soak up input before opening output for writing

[Chris Wesseling]

Change by Chris Wesseling <chris.wesseling at protonmail.com>:


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pull_requests: +27537
pull_request: https://github.com/python/cpython/pull/29273

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45644>
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