chore(docs): add SM 3.12 to comp matrix

Author: Michal-Leszczynski

docs/source/compatibility-matrix.rst

@@ -9,6 +9,8 @@ The following table shows which version of ScyllaDB Manager supports which versi
 
    * - ScyllaDB Manager Version
      - ScyllaDB Version
+   * - 3.12
+     - 2025.1, 2025.4, 2026.1, 2026.2
    * - 3.11
      - 2025.1, 2025.4, 2026.1, 2026.2
    * - 3.10