[Anon] Tomb Guardians (1b): Unit Group not accounting for multiple units in the group

**Problem:**
Unit Group not accounting for multiple units in the group

**Expected:**
The costs and warband rating should increase for every additional model in the group

No file, test, or entry point is named in the issue. Locate the Tomb Guardians Unit Group definition, inspect how additional models affect costs and warband rating, and verify that both values increase for every added model.

Written by the indexing model from the issue text.