Cabal uses source files from `.` even when `.` is not listed under `hs-source-dirs`

**To Reproduce**

```
$ tree
.
├── foo.cabal
├── Foo.hs
└── src
└── Foo.hs

2 directories, 3 files
```

```cabal
cabal-version: 3.8
-- foo.cabal
name: foo
version: 0.0.0

library
build-depends: base
hs-source-dirs: src
exposed-modules: Foo
```

```haskell
-- src/Foo.hs
module Foo where

foo :: Int
foo = 23
```

```haskell
-- Foo.hs
module Foo where

foo :: Int
foo = "bar"
```

```
$ cabal build

Foo.hs:4:7: error: [GHC-83865]
• Couldn't match type ‘[Char]’ with ‘Int’
Expected: Int
Actual: String
• In the expression: "bar"
In an equation for ‘foo’: foo = "bar"
|
4 | foo = "bar"
| ^^^^^
Error: cabal: Failed to build foo-0.0.0.
```

**Expected behavior**
`cabal build` succeeds.

**System information**
- cabal 3.10.1.0 / ghc 9.6.2 / Linux

Start by reproducing the issue with foo.cabal, Foo.hs, and src/Foo.hs, then run cabal build. Trace Cabal's source-file discovery and hs-source-dirs handling to determine why the root Foo.hs is compiled. Done means the example builds successfully while using only the declared src directory.

Written by the indexing model from the issue text.