gh-111684: Avoid a Compiler Warning

[ericsnowcurrently]

gh-111671 introduced a compiler warning about an unused function, which I'm fixing here.

• Issue: New warning: "‘_session_is_active’ defined but not used [-Wunused-function]" #111684

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x RHEL8 LTO 3.x has failed when building commit df9815e.

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/567/builds/5212) and take a look at the build logs.
4. Check if the failure is related to this commit (df9815e) 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/567/builds/5212

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

==

Click to see traceback logs

remote: Enumerating objects: 7, done.        
remote: Counting objects:  14% (1/7)        
remote: Counting objects:  28% (2/7)        
remote: Counting objects:  42% (3/7)        
remote: Counting objects:  57% (4/7)        
remote: Counting objects:  71% (5/7)        
remote: Counting objects:  85% (6/7)        
remote: Counting objects: 100% (7/7)        
remote: Counting objects: 100% (7/7), done.        
remote: Compressing objects: 100% (1/1)        
remote: Compressing objects: 100% (1/1), done.        
remote: Total 4 (delta 3), reused 3 (delta 3), pack-reused 0        
From https://github.com/python/cpython
 * branch                  main       -> FETCH_HEAD
Note: switching to 'df9815eb11b58dfaae02a8e3fb85ae8aa725dc17'.

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 df9815eb11 gh-111684: Avoid a Compiler Warning (gh-111706)
Switched to and reset branch 'main'

make: *** [Makefile:2067: buildbottest] Error 3