gh-123229: Fix valgrind warning by initializing the f-string buffers to 0 in the tokenizer

[pablogsal]

• Issue: New valgrind warning in Python 3.12.5 #123229

[miss-islington-app]

Thanks @pablogsal for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-123264 is a backport of this pull request to the 3.13 branch.

[miss-islington-app]

Sorry, @pablogsal, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker adc5190014efcf7b7a4c5dfc9998faa8345527ed 3.12

[bedevere-app]

GH-123265 is a backport of this pull request to the 3.12 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot PPC64LE RHEL8 Refleaks 3.12 has failed when building commit 7dec3d7.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1158/builds/466) and take a look at the build logs.
4. Check if the failure is related to this commit (7dec3d7) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1158/builds/466

Summary of the results of the build (if available):

Click to see traceback logs

remote: Enumerating objects: 10, done.        
remote: Counting objects:  10% (1/10)        
remote: Counting objects:  20% (2/10)        
remote: Counting objects:  30% (3/10)        
remote: Counting objects:  40% (4/10)        
remote: Counting objects:  50% (5/10)        
remote: Counting objects:  60% (6/10)        
remote: Counting objects:  70% (7/10)        
remote: Counting objects:  80% (8/10)        
remote: Counting objects:  90% (9/10)        
remote: Counting objects: 100% (10/10)        
remote: Counting objects: 100% (10/10), done.        
remote: Compressing objects:  16% (1/6)        
remote: Compressing objects:  33% (2/6)        
remote: Compressing objects:  50% (3/6)        
remote: Compressing objects:  66% (4/6)        
remote: Compressing objects:  83% (5/6)        
remote: Compressing objects: 100% (6/6)        
remote: Compressing objects: 100% (6/6), done.        
remote: Total 10 (delta 4), reused 10 (delta 4), pack-reused 0 (from 0)        
From https://github.com/python/cpython
 * branch                  3.12       -> FETCH_HEAD
Note: switching to '7dec3d7acbb072e0d5cd7357c1ddf12d3c667e8a'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 7dec3d7acb [3.12] gh-123229: Fix valgrind warning by initializing the f-string buffers to 0 in the tokenizer (GH-123263) (#123265)
Switched to and reset branch '3.12'

make: *** [Makefile:2021: buildbottest] Terminated