bpo-35721: Close socket pair if Popen in _UnixSubprocessTransport fails (GH-11553)



This slightly expands an existing test case `test_popen_error` to trigger a `ResourceWarning` and fixes it.


https://bugs.python.org/issue35721
diff --git a/Misc/ACKS b/Misc/ACKS
index 8b32325..77f1990 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -486,6 +486,7 @@
 John Feuerstein
 Carl Feynman
 Vincent Fiack
+Niklas Fiekas
 Anastasia Filatova
 Tomer Filiba
 Segev Finer