Unexpected dependency differences when using --enable-multi-repl

## Describe the bug

Cabal-syntax, Cabal, and cabal-doctest are added to the list of dependencies when --enable-multi-repl is added to the cabal command line.

```
[b@kuusi:~/src/haskell/amazonka]$ cabal repl amazonka-core
Build profile: -w ghc-9.6.6 -O1
In order, the following will be built (use -v for more details):
- amazonka-core-2.0 (interactive) (lib) (configuration changed)
Configuring library for amazonka-core-2.0...
Preprocessing library for amazonka-core-2.0...
GHCi, version 9.6.6: https://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/b/Projects/dotfiles/ghci
[ 1 of 31] Compiling Amazonka.Core.Lens.Internal ( src/Amazonka/Core/Lens/Internal.hs, interpreted )
[ 2 of 31] Compiling Amazonka.Prelude ( src/Amazonka/Prelude.hs, interpreted )
[ 3 of 31] Compiling Amazonka.Crypto ( src/Amazonka/Crypto.hs, interpreted )
^CInterrupted.
||
λ
Leaving GHCi.

[b@kuusi:~/src/haskell/amazonka]$ cabal repl --enable-multi-repl amazonka-core
Warning: The package list for 'hackage.haskell.org' is 67 days old.
Run 'cabal update' to get the latest list of available packages.
Resolving dependencies...
Build profile: -w ghc-9.6.6 -O1
In order, the following will be built (use -v for more details):
- Cabal-syntax-3.12.1.0 (lib) (requires build)
- Cabal-3.12.1.0 (lib) (requires build)
- cabal-doctest-1.0.11 (lib) (requires build)
- xml-conduit-1.9.1.4 (lib:xml-conduit) (requires build)
- amazonka-core-2.0 (interactive) (lib) (configuration changed)
Starting Cabal-syntax-3.12.1.0 (lib)
^C

```

**But wait, there's more!** Why is xml-conduit being built? Why doesn't it already exist in a ready-to-use format? amazonka-core depends on it. It exists in ~/.cabal/store/ghc-9.6.6.

## To Reproduce
???

## Expected behavior

I would expect the same dependencies to be needed whether or not --enable-multi-repl is added.

## System information
- NixOS 24.11
- Cabal 3.12.1.0
- GHC 9.6.6

Start by reproducing the two cabal repl commands from the issue on Cabal 3.12.1.0 with GHC 9.6.6, then compare their dependency plans and investigate why --enable-multi-repl adds Cabal-syntax, Cabal, cabal-doctest, and xml-conduit. Done means the differing dependencies are explained and the expected behavior is addressed.

Written by the indexing model from the issue text.