Config file read twice if $CWD is same as config dir, e.g. $HOME

If a user runs from the $HOME directory (or any of the configuration directories), where a config file exists, the `$CWD/` is found, in addition to the `/`. E.g. `$HOME/.syft.yaml` exists, and syft is run from `$HOME`, the same file is read twice.

See: https://github.com/anchore/syft/issues/4322

The issue names no repository files or tests; begin by tracing the configuration-file discovery and loading path that checks $CWD and configuration directories. Reproduce the case where $HOME/.syft.yaml is found from $HOME, then verify that the same file is loaded only once and cover that behavior with a regression test.

Written by the indexing model from the issue text.