try to use the same str object for all code filenames when compiling or unmarshalling (#12190)

This should reduce memory usage.
diff --git a/Misc/NEWS b/Misc/NEWS
index 0514c96..df8bca8 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #12190: Try to use the same filename object when compiling unmarshalling
+  a code objects in the same file.
+
 - Issue #12166: Move implementations of dir() specialized for various types into
   the __dir__() methods of those types.