Flaky PAM integration tests `TestExecModule` and `TestGdmModule` fail very frequently on s390x

The launchpad build of authd 0.5.3 for the s390x architecture keeps failing. I retried the build 3 times. The logs are lost unless saved before retrying, so I only have the logs of two builds:
* [Build 1](https://github.com/user-attachments/files/20721469/tmpgsxg386n.txt)
* [Build 2](https://github.com/user-attachments/files/20721509/tmp8_nefg3t.txt)

In both cases, it's the github.com/ubuntu/authd/pam/integration-tests which fails, once with "fatal error: unknown caller pc" and once with "fatal error: invalid pointer found on stack".

EDIT: Both of these were `TestExecModule`

Start in github.com/ubuntu/authd/pam/integration-tests and inspect TestExecModule and TestGdmModule, then compare the two attached s390x build logs. Reproduce the Launchpad authd 0.5.3 build if possible and determine why the tests produce the reported Go runtime failures; done means the affected integration tests no longer fail frequently on s390x.

Written by the indexing model from the issue text.