Fix spotify soloist new download (#6176)

# What does this implement/fix?

Fixes Spotify Soloist integration after they changed their install tar
to include several other files that are not currently filtered
(CHANGELOG.md, THIRD_PARTY_LICENSES.txt, etc.). Now we look for a file
named `soloist` and then check to see that it is a regular file before
continuing.

~Additionally, after I resolved this error and launched locally, I run
into a PulseAudio error because it writes its cookie to home and I was
using a non-root container to run music-assistant.~

Note when I ran locally, pytest had 4 unrelated errors to my changes.
I'm guessing these are pre-existing failures or something to do with my
dev environment?

The tests around my code all pass when I tested.

**Related issue (if applicable):**

- https://github.com/music-assistant/support/issues/6301

## Types of changes

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- [x] Bugfix (non-breaking change which fixes an issue) — `bugfix`
- [ ] New feature (non-breaking change which adds functionality) —
`new-feature`
- [ ] Enhancement to an existing feature — `enhancement`
- [ ] New music/player/metadata/plugin provider — `new-provider`
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected) — `breaking-change`
- [ ] Refactor (no behaviour change) — `refactor`
- [ ] Documentation only — `documentation`
- [ ] Maintenance / chore — `maintenance`
- [ ] CI / workflow change — `ci`
- [ ] Dependencies bump — `dependencies`

## Checklist

- [x] The code change is tested and works locally.
- [x] `pre-commit run --all-files` passes.
- [x] `pytest` passes, and tests have been added/updated under `tests/`
where applicable.
- [ ] (N/A) For changes to shared models, the companion PR in
`music-assistant/models` is linked.
- [ ] (N/A) For changes affecting the UI, the companion PR in
`music-assistant/frontend` is linked.
- [x] I have read and complied with the project's [AI
Policy](https://github.com/music-assistant/.github/blob/main/AI_POLICY.md)
for any AI-assisted contributions.
- [ ] (N/A) I have [raised a PR against the documentation
repository](https://github.com/music-assistant/music-assistant.io/blob/main/CONTRIBUTING.md)
targeting the main or beta branch as appropriate.