doc: Mesh maturity to supported for nRF54L15

Changed the software maturity level for Bluetooth Mesh
to Supported for the nRF54L15.

Signed-off-by: Ingar Kulbrandstad <[email protected]>

Author: Balaklaka

doc/nrf/releases_and_maturity/software_maturity.rst

@@ -211,7 +211,7 @@ The following table indicates the software maturity levels of the support for ea
      - Supported
      - Supported
      - --
-     - Experimental
+     - Supported
      - --
      - --
      - --