CI: Disambiguate Windows MSI installer name

Previously, this Windows MSI installer was lumped into the same artifact name
as the general Windows binary distribution (e.g.,
`cryptol-3.2.0.99-windows-2019-X64 (GHC 9.4.8)`). As of `v4` of GitHub Actions'
`upload-artifact`, however, it is an error to have two separate
`upload-artifact` steps share the same artifact name. As such, we have to
disambiguate the Windows installer artifact, which this patch accomplishes.

.github/workflows/ci.yml

@@ -244,7 +244,7 @@ jobs:
       - uses: actions/upload-artifact@v4
         if: runner.os == 'Windows'
         with:
-          name: ${{ env.NAME }} (GHC ${{ matrix.ghc-version }})
+          name: Windows MSI installer (GHC ${{ matrix.ghc-version }})
           path: "cryptol.msi*"
           if-no-files-found: error
           retention-days: ${{ needs.config.outputs.retention-days }}