bpo-36447, bpo-36447: Fix refleak in _PySys_InitMain() (GH-12586)

Fix refleak in sysmodule.c when calling SET_SYS_FROM_STRING_BORROW.
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 1af11c4..3de94e8 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -2635,6 +2635,7 @@
         return -1;
     }
     SET_SYS_FROM_STRING_BORROW("_xoptions", xoptions);
+    Py_DECREF(xoptions);
 
 #undef COPY_LIST
 #undef SET_SYS_FROM_WSTR