[Feature] Add tests for installing local package when symlinks are not supported by the OS

### Housekeeping

- [X] I am a maintainer of dbt-core

### Short description

We are not currently testing the case where the user's operating system (OS) doesn't support symlinks. As a result, we could accidentally break these code paths in the future.

So we'd like to add functional tests for scenarios like https://github.com/dbt-labs/dbt-core/issues/9719 _specifically_ when the OS running dbt does not support symlinks.

Create a `packages.yml` file:
```yaml
packages:
- local: ../
```

Then install it:

```shell
dbt deps
```

### Acceptance criteria

There are functional tests that cover the code paths when a user's operating system doesn't support symlinks (which is used for [local package dependencies](https://docs.getdbt.com/docs/build/packages#local-packages) when running `dbt deps`).

### Suggested Tests

We don't know how exactly to test it currently, so this would be something to brainstorm and choose an approach.

### Impact to Other Teams

None.

### Will backports be required?

It would probably be wise to backport to supported versions of dbt-core to avoid accidentally missing regressions when merging _other_ backports!

### Context

This was discovered during review of https://github.com/dbt-labs/dbt-core/pull/9734.