devel/py-backports.zoneinfo: unbreak build with py310+ (+)

We already have Python 3.7 as minimal supported release, so
force #ifdef's for 3.7+ API as always positive to prevent use deprecated types

While here, port upstream patch for MR#97 (https://github.com/pganssle/zoneinfo/pull/97)
"Decrement the refcount of _PyLong_One in the correct branch"