[issue37309] idlelib/NEWS.txt for 3.9.0 and backports

[Terry J. Reedy]

Change by Terry J. Reedy <tjreedy at udel.edu>:


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pull_requests: +20754
pull_request: https://github.com/python/cpython/pull/21612

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37309>
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