fix(detectors): handle dirs that are not dirs for dotnet

[elsapet]

Description

We were getting errors from dotnet when scanning a file and not a directory e.g.

{
  "file": "",
  "message": "accept dir failed for detector dotnet: fdopendir /Users/elsapet/Bearer/api-management-app/db/seed/policy_engine/policy_templates.json: not a directory",
  "type": "error"
}

To fix, we add a check for whether a given path leads to a directory or a single file, and handle as appropriate.

Checklist

• I've added test coverage that shows my fix or feature works as expected.
• I've updated or added documentation if required.
• I've included usage information in the description if CLI behavior was updated or added.
• PR title follows Conventional Commits format

[swarmia]

✅  Linked to AMA-3065 · dotnet detector errors when it shouldn't
➡️  Part of AMA-2947 · OSS - Curio CLI

[elsapet]

@vjerci Any guidance on how to add a test for this case?

[spdawson]

👍 Looks good to me; though of course you may want to wait for a review from someone more familiar with Go 🙂