gh-117657: use relaxed loads for checking dict keys immortality

[DinoV]

Checking for immortality of dict keys is reported as a TSAN violation, we just need relaxed loads

• Issue: Make TSAN tests pass with the GIL disabled in free-threaded builds #117657

[colesbury]

LGTM

[colesbury]

We could also do dk == Py_EMPTY_KEYS and avoid the atomics, but this seems fine too.

[DinoV]

I kind of like that, but am a little worried that it'll be overlooked if any other keys become immortal, so I'll just keep it as-is for now.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 RHEL7 LTO 3.x has failed when building commit 1e4a4c4.

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/all/#builders/507/builds/7247) and take a look at the build logs.
4. Check if the failure is related to this commit (1e4a4c4) 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/all/#builders/507/builds/7247

Failed tests:

• test_capi

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

==

Click to see traceback logs

remote: Enumerating objects: 7, done.        
remote: Counting objects:  16% (1/6)        
remote: Counting objects:  33% (2/6)        
remote: Counting objects:  50% (3/6)        
remote: Counting objects:  66% (4/6)        
remote: Counting objects:  83% (5/6)        
remote: Counting objects: 100% (6/6)        
remote: Counting objects: 100% (6/6), 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 7 (delta 0), reused 2 (delta 0), pack-reused 1        
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HEAD is now at 1e4a4c4... gh-117657: use relaxed loads for checking dict keys immortality (#118067)
Switched to and reset branch 'main'

make: *** [Makefile:2229: buildbottest] Error 2