fix: use the correct layer for new gemma scope SAE sparsities

[hijohnnylin]

Description

Fixes the incorrect layer 5 and uses the correct layer 12 for sparsity experiment instead.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 65.84%. Comparing base (ae345b6) to head (a78b93e). Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #348 +/- ## ======================================= Coverage 65.84% 65.84% ======================================= Files 25 25 Lines 3288 3288 Branches 421 421 ======================================= Hits 2165 2165 Misses 1009 1009 Partials 114 114 ```

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