[change-detect] log helpful error message when git history is not available

### TL;DR

Change detection in guardian requires fetch-depth on the checkout action. When this requirement isn't met a generic error message is shown to the user. Instead we should detect whether the history is there and log a message suggesting adding the fetch-depth.

### Detailed design

Current error message looks like:

```
fatal: ambiguous argument 'HEAD~1': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git [...] -- [...]'
dirname: missing operand
Try 'dirname --help' for more information.
Error: Process completed with exit code 123.
```

Look for the change detection logic in the codebase, likely in a command or utility that runs git commands. Find where the error 'HEAD~1' is used. Add a check for git history availability before that command and log a helpful message about setting fetch-depth. Run the guardian CLI in a test environment without full git history to verify the new error message appears.

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