bpo-39573: Fix bad copy-paste in Py_SET_SIZE.

[brandtbucher]

@vstinner

https://bugs.python.org/issue39573

[vstinner]

I also noticed a typo in Py_SET_SIZE() doc:
https://docs.python.org/dev/c-api/structures.html#c.Py_SET_SIZE

"Set the object o size of size." => "Set ... to size."

Would you mind to also fix it, please?

[codecov]

Codecov Report

Merging #18496 into master will increase coverage by 1.09%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #18496 +/- ##
===========================================
+ Coverage 82.10% 83.20% +1.09% 
===========================================
Files 1958 1571 -387 Lines 589576 414668 -174908 Branches 44449 44450 +1 ===========================================
- Hits 484095 345007 -139088 + Misses 95833 60017 -35816 + Partials 9648 9644 -4 

Impacted Files	Coverage Δ
Lib/distutils/tests/test_bdist_rpm.py	30.00% <0.00%> (-65.00%)	⬇️
Lib/distutils/command/bdist_rpm.py	7.63% <0.00%> (-56.88%)	⬇️
Lib/test/test_urllib2net.py	76.92% <0.00%> (-13.85%)	⬇️
Lib/test/test_smtpnet.py	78.57% <0.00%> (-7.15%)	⬇️
Lib/ftplib.py	63.85% <0.00%> (-6.06%)	⬇️
Lib/test/test_ftplib.py	87.11% <0.00%> (-4.72%)	⬇️
Tools/scripts/db2pickle.py	17.82% <0.00%> (-3.97%)	⬇️
Tools/scripts/pickle2db.py	16.98% <0.00%> (-3.78%)	⬇️
Lib/test/test_socket.py	71.94% <0.00%> (-3.77%)	⬇️
Lib/test/test_asyncio/test_base_events.py	91.84% <0.00%> (-3.30%)	⬇️
... and 442 more

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[vstinner]

Thanks. I'm feeling ashamed by these typos, but I'm also feeling better after your fix :-)

[brandtbucher]

Thanks! Besides, maybe there's some use-case out there for Py_SIZE(o) == Py_REFCNT(o)! 😉