Cabal doesn't rebuild as much as it should after "mixins:" section is changed in .cabal file

**Describe the bug**

A change in the `mixins:` section of a cabal file, that should trigger a compilation error when invoking `cabal build`, doesn't trigger the error.

**To Reproduce**

Clone this repo https://github.com/danidiaz/orphans/tree/a7818653c635cfd80dc481914713e1b28392b5fc

Invoke `cabal v2-build`. It should compile correctly.

Now, in the `mixins:` section of the executable, change the lines:

mixins:
foo (Foo as Foo1) requires (Foo.Sig as Foo.Sig1),
foo (Foo as Foo2) requires (Foo.Sig as Foo.Sig2)

into the lines:

mixins:
foo (Foo as Foo1) requires (Foo.Sig as Foo.Sig1),
foo (Foo as Foo2) requires (Foo.Sig as Foo.Sig1)

then invoke `cabal v2-build` again.

This second invocation doesn't give an error.

**Expected behavior**

The second invocation of `cabal v2-build` *should* fail, with an error like:

Main.hs:7:10: error:
Duplicate instance declarations:
instance Show Foo2.Foo -- Defined at Main.hs:7:10
instance Show Foo2.Foo -- Defined at Main.hs:10:10
|
7 | instance Show Foo1.Foo where

This is because the `foo` library has been instantiated twice in the exact same way, so `Foo1.Foo` and `Foo2.Foo` are the same type.

If between making the change in the .cabal file and running `cabal v2-build` for the second time we invoke `cabal v2-clean`, the error shows up as it should.

cabal v2-clean
cabal v2-build

**System information**
- Windows
- cabal-install version 3.2.0.0
- compiled using version 3.2.0.0 of the Cabal library
- The Glorious Glasgow Haskell Compilation System, version 8.10.1