a7800 is not building with Python 3.9 and newer

[smesgr9000]

A7800 is not building with Python3.9 or newer with the following error:

Traceback (most recent call last):
File "/home/sme/code/atari7800/a7800/scripts/build/msgfmt.py", line 291, in
main()
File "/home/sme/code/atari7800/a7800/scripts/build/msgfmt.py", line 287, in main
make(filename, outfile)
File "/home/sme/code/atari7800/a7800/scripts/build/msgfmt.py", line 254, in make
output = generate()
^^^^^^^^^^
File "/home/sme/code/atari7800/a7800/scripts/build/msgfmt.py", line 115, in generate
output += array.array("i", offsets).tostring()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'array.array' object has no attribute 'tostring'

this duplicate function was removed in 3.9 see: https://docs.python.org/3.9/whatsnew/3.9.html#removed

diff --git a/scripts/build/msgfmt.py b/scripts/build/msgfmt.py
index deb02ae3..a00596f6 100644
--- a/scripts/build/msgfmt.py
+++ b/scripts/build/msgfmt.py
@@ -112,7 +112,7 @@ def generate():
                          7*4,               # start of key index
                          7*4+len(keys)*8,   # start of value index
                          0, 0)              # size and offset of hash table
-    output += array.array("i", offsets).tostring()
+    output += array.array("i", offsets).tobytes()
     output += ids
     output += strs
     return output

fixes this issue