[3.13] gh-124832: Add a note to indicate that `datetime.now` may return the same...

[3.13] gh-124832: Add a note to indicate that `datetime.now` may return the same instant (GH-124834) (#125145)

gh-124832: Add a note to indicate that `datetime.now` may return the same instant (GH-124834)

* Update datetime.rst

* Update datetime.rst

replace warning with note

* Update Doc/library/datetime.rst

* Update Doc/library/datetime.rst

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(cherry picked from commit 760b1e103a0aa696cdf448e0d500cd1bac2213fa)

Co-authored-by: spacemanspiff2007 <10754716+spacemanspiff2007@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>