[issue38488] Update bundled pip to 19.3

[STINNER Victor]

Change by STINNER Victor <vstinner at python.org>:


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keywords: +patch
pull_requests: +19733
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/20484

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38488>
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