Build tool not rerun when build tool version changes

Reproducer using cabal-3.16.1.0 (latest release):

Step 1: using alex-3.4
```
cabal get java-adt-1.0.20251105
cd java-adt-*
cabal build -c 'any.alex==3.4.*'
```
This errors:
```
dist-newstyle/build/aarch64-osx/ghc-9.8.4/java-adt-1.1/x/java-adt/build/java-adt/java-adt-tmp/Lexer.hs:771:25: error: [GHC-87543]
Ambiguous occurrence ‘fromString’.
It could refer to
either ‘String1.fromString’,
imported from ‘String1’ at src/Lexer.x:3:26-35,
or ‘GHC.Exts.fromString’,
imported from ‘GHC.Exts’ at dist-newstyle/build/aarch64-osx/ghc-9.8.4/java-adt-1.1/x/java-adt/build/java-adt/java-adt-tmp/Lexer.hs:20:1-15
(and originally defined in ‘Data.String’).
|
771 | alex_action_21 = TkId . fromString
| ^^^^^^^^^^
```
(Cf. https://hackage.haskell.org/package/java-adt-1.0.20251105/reports/2)

Step 2: using alex-3.5
```
cabal build -c 'any.alex==3.5.*'
```
Still fails with the same error.

Step 3: using alex-3.5 after cleaning
```
rm -rf dist-newstyle
cabal build -c 'any.alex==3.5.*'
```
Succeeds.

This shows that `Lexer.hs` is not regenerated by `alex` when its version is changed.
This is an unsoundness in the "recompilation" checker of cabal.