ci: Version of cabal-install installed by setup-haskell should be specified precisely

At the moment the `latest` version of `cabal-install` is installed for validate jobs.

```
- name: Install primary compiler
uses: haskell-actions/setup@v2
id: setup-haskell
with:
ghc-version: ${{ env.GHC_FOR_RELEASE }}
cabal-version: latest
```

This had the effect of completely breaking CI when the definition of "latest" changed. It would be better to explicitly pin a specific version of cabal-install here and update it in a controlled manner.

See #10172

Start by locating the validate-job workflow containing the setup-haskell step shown in the issue, then review #10172 for the CI breakage context. Replace the floating cabal-version setting with a precise version and verify that the validate jobs run successfully with the pinned cabal-install version.

Written by the indexing model from the issue text.