FIX: some code smells found by clang-tidy

[reneme]

Introduced in the example code of #4043.

[coveralls]

coverage: 91.837% (+0.001%) from 91.836%
when pulling 65a6dc5 on Rohde-Schwarz:fix/clang-tidy
into 1644599 on randombit:master.

[randombit]

Thanks

Are we not running clang-tidy on the examples in CI?

Edit: indeed it seems this was skipped in the clang-tidy run https://github.com/randombit/botan/actions/runs/9209158585/job/25333053746 but looking at the relevant scripts I don't see why

[reneme]

Are we not running clang-tidy on the examples in CI?

Fixed here: 0c886a4
Problem was, that the CI's clang-tidy job did not enable 'examples' in the build configuration (among other things). The run_clang_tidy.py is consulting compile_commands.json for files to be evaluated: which only lists files in components that were actually enabled in the build configuration. Therefore, examples were not clang-tidy'ed in CI before.