"Error: cabal: There is no <pkgname>.cabal package file or cabal.project file." in directory with .cabal file

**Describe the bug**
`cabal build` gives a very confusing error message in a (unknown) package subdirectory under a cabal.project.

**To Reproduce**
1. have a project with cabal.project
2. in a tmp/ subdir unpack a cabal package
3. try to build said package:

```
Error: cabal: There is no .cabal package file or cabal.project file.
To build packages locally you need at minimum a .cabal file. You can
use 'cabal init' to create one.
```
but there is a .cabal file right there!

**Expected behavior**
Package in unrelated subdir to build normally.
Also complaining there is no .cabal file is rather confusing.

**System information**
- Operating system: Fedora Linux
- `cabal-3.8+`, `ghc-9.4`

**Additional context**
Currently used by hkgr to do pristine sanity builds from tarball before publishing to Hackage.

Related discussion: #8519