InfoItem.lastChangeDate/lastChangeDateTime returns wrong date when cloning shallow repository

### Affected version

2.1.0

### Bug description

When cloning a [shallow Git repository](https://git-scm.com/docs/shallow) (i.e. with [`--depth=1`](https://git-scm.com/docs/git-fetch#Documentation/git-fetch.txt---depthdepth), common for CI builds like GitHub actions,https://github.com/actions/checkout) the date being returned by `InfoItem.lastChangeDate/lastChangeDateTime` incorrectly always returns the author date of that last commit (which was not necessarily affecting the file to which the metadata belongs).

There should at least be a warning in that case as otherwise issues related to that are hard to track.

This relates to #1134

Start by tracing the implementations of InfoItem.lastChangeDate and lastChangeDateTime, then inspect how shallow Git repositories are detected during metadata lookup. Check the behavior with a repository cloned using --depth=1. Done means the incorrect date case is addressed or clearly warned about, with existing relevant tests updated or added if the project has coverage for this path.

Written by the indexing model from the issue text.