#15040: Close files in mailbox tests for PyPy compatibility

Original patch by Matti Picus.
diff --git a/Misc/ACKS b/Misc/ACKS
index 958951f..88b7ed0 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -762,6 +762,7 @@
 Adrian Phillips
 Christopher J. Phoenix
 Neale Pickett
+Matti Picus
 Jim St. Pierre
 Dan Pierson
 Martijn Pieters
diff --git a/Misc/NEWS b/Misc/NEWS
index c5eaa9c..5052009 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -435,6 +435,9 @@
 Tests
 -----
 
+- Issue #15040: Close files in mailbox tests for PyPy compatibility.
+  Original patch by Matti Picus.
+
 - Issue #15802: Fix test logic in TestMaildir.test_create_tmp. Patch
   by Serhiy Storchaka.