cabal fetch doesn't fetch multiple package versions

**Describe the bug**

`cabal fetch` appears to nub requested packages by package name.

**To Reproduce**
```
$ rm ~/.cabal/packages/hackage.haskell.org/lens/* -R
$ cabal fetch lens-4.18 lens-4.17.1 --no-dependencies
Downloading lens-4.17.1
Downloaded lens-4.17.1
```
Note how `lens-4.18` is not fetched. This [breaks](https://gitlab.haskell.org/ghc/head.hackage/issues/6) `head.hackage` .

**Expected behavior**
Both `lens-4.17.1` and `lens-4.18` are fetched.

**System informataion**

```
$ cabal --version
cabal-install version 3.0.0.0
compiled using version 3.0.0.0 of the Cabal library
```