bpo-38803: Fix leak in posixmodule

[eduardo-elizondo]

Fixed a leak in posixmodule by running my leak detection tool:

eelizondo@build -> ./python -m test test_wait3 -R 3:3 -j0
Expected refcnt: 24, actual: 25
class 'resource.struct_rusage'>

This quickly pointed out to the function that pulled out the struct_rusage class.

Run after the fix:

eelizondo@build -> ./python -m test test_wait3 -R 3:3 -j0
0:00:42 load avg: 4.16 [1/1] test_wait3 passed (42.3 sec)
beginning 6 repetitions
123456
123456
......
== Tests result: SUCCESS ==

eelizondo@build -> ./python -m test test_wait4 -R 3:3 -j0
0:00:00 load avg: 3.59 Run tests in parallel using 50 child processes
0:00:30 load avg: 4.02 running: test_wait4 (30.0 sec)
0:00:36 load avg: 4.10 [1/1] test_wait4 passed (36.3 sec)
beginning 6 repetitions
123456
......
== Tests result: SUCCESS ==

https://bugs.python.org/issue38803

[eduardo-elizondo]

cc @vstinner

[corona10]

@eduardo-elizondo cc @vstinner

Thanks for your contribution.
I checked your PR locally and it works well.

master

Python 3.9.0a1+ (heads/master:27fc3b6, Nov 25 2019, 17:29:57

$ ./python -m test test_wait3 -R 3:3 -j0
0:00:00 load avg: 0.00 Run tests in parallel using 10 child processes
0:00:30 load avg: 0.00 running: test_wait3 (30.0 sec)
0:00:36 load avg: 0.00 [1/1/1] test_wait3 failed (36.6 sec)
beginning 6 repetitions
123456
......
test_wait3 leaked [23, 22, 22] references, sum=67

== Tests result: FAILURE ==

1 test failed:
    test_wait3

Total duration: 36.9 sec
Tests result: FAILURE

Proposed

Python 3.9.0a1+ (heads/pr/17373:b67e20e, Nov 25 2019, 17:27:28)

$ ./python -m test test_wait3 -R 3:3 -j0
0:00:00 load avg: 0.00 Run tests in parallel using 10 child processes
0:00:30 load avg: 0.00 running: test_wait3 (30.0 sec)
0:00:36 load avg: 0.00 [1/1] test_wait3 passed (36.6 sec)
beginning 6 repetitions
123456
......

== Tests result: SUCCESS ==

1 test OK.

Total duration: 37.0 sec
Tests result: SUCCESS