Unbreak torture_config_make_absolute() on OpenBSD

The torture_config_make_absolute() and its _no_sshdir() version both segfault on OpenBSD. The reason for this is that the storage returned by getpwuid() is backed by mmap and is unapped by the getpwnam() call in ssh_path_expand_tilde(), so a later access to home segfaults. The possibility of this happening (getpwnam() overwriting values returned by getpwuid()) is explicitly called out in POSIX.

A simple fix is to work with copies of username and homedir.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• Code modified for feature
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code

Summary by Sourcery

Prevent segfaults in torture_config_make_absolute unit tests on OpenBSD by copying passwd data instead of referencing potentially unmapped memory

Bug Fixes:

• Fix torture_config_make_absolute tests to avoid use-after-unmap of getpwuid data on OpenBSD by duplicating pw_name and pw_dir before use

Tests:

• Add strdup calls and corresponding frees for user and home variables in torture_config_make_absolute tests to ensure valid memory handling