gh-120385: Fix reference leak in symtable

[Eclips4]

• Issue: test_coroutines leaks references #120385

[vstinner]

LGTM. I confirm that the change fix the refleak.

Without this change, ./python -m test -R 3:3 test_coroutines leaks. With this change, it no longer leaks.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Fedora Stable LTO + PGO 3.x has failed when building commit 19435d2.

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/29/builds/6440) and take a look at the build logs.
4. Check if the failure is related to this commit (19435d2) 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/29/builds/6440

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:  10% (1/10)        
remote: Compressing objects:  20% (2/10)        
remote: Compressing objects:  30% (3/10)        
remote: Compressing objects:  40% (4/10)        
remote: Compressing objects:  50% (5/10)        
remote: Compressing objects:  60% (6/10)        
remote: Compressing objects:  70% (7/10)        
remote: Compressing objects:  80% (8/10)        
remote: Compressing objects:  90% (9/10)        
remote: Compressing objects: 100% (10/10)        
remote: Compressing objects: 100% (10/10), done.        
remote: Total 10 (delta 1), reused 7 (delta 0), pack-reused 0        
From https://github.com/python/cpython
 * branch                  main       -> FETCH_HEAD
Note: switching to '19435d299a1fae9ad9a6bbe6609e41ddfd7f6cbe'.

You are in 'detached HEAD' state. You can look around, make experimental
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  git switch -c <new-branch-name>

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

HEAD is now at 19435d299a gh-120385: Fix reference leak in symtable (#120386)
Switched to and reset branch 'main'

configure: WARNING: no system libmpdecimal found; falling back to bundled libmpdecimal (deprecated and scheduled for removal in Python 3.15)

find: ‘build’: No such file or directory
find: ‘build’: No such file or directory
find: ‘build’: No such file or directory
find: ‘build’: No such file or directory
make[2]: [Makefile:3123: clean-retain-profile] Error 1 (ignored)
ar: unable to copy file 'libpython3.14.a'; reason: Success
make[2]: *** [Makefile:1047: libpython3.14.a] Error 1
make[1]: *** [Makefile:877: profile-gen-stamp] Error 2
make: *** [Makefile:889: profile-run-stamp] Error 2

[JelleZijlstra]

Thanks for the fix! Sorry I forgot to run the buildbots before merging my change.