[3.13] gh-118201: Simplify conv_confname (#126089)

[mhsmith]

(cherry picked from commit c5c9286)

This wasn't originally backported because the failure wasn't happening on the 3.13 branch, but now it's happened twice in the last week:

• https://buildbot.python.org/#/builders/1590/builds/504
• https://buildbot.python.org/#/builders/1590/builds/507

The fix has been on the main branch for several months now, and the failure hasn't happened there again on either Android or iOS.

• Issue: Intermittent "unrecognized configuration name" failure on iOS and Android #118201

[mhsmith]

!buildbot android|ios

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @mhsmith for commit 9466eb8 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F131375%2Fmerge

The command will test the builders whose names match following regular expression: android|ios

The builders matched are:

• AMD64 Android PR
• aarch64 Android PR
• iOS ARM64 Simulator PR

[freakboy3742]

👍 Looks like a fairly vanilla back port (that is only complicated by the generated portions); and the stability of the change on the main branch (plus the ABI stability check on CI for this PR) suggests it's having the desired effect.