manifest: update picolibc to avoid setting of CMAKE_BUILD_TYPE

This commit updates picolibc module so that CMAKE_BUILD_TYPE is not
defined by picolibc when building with Zephyr.

The avoids a situation where both picolibc and Zephyr defines the
optimization level, for example like: `-Os -O2`.

And remove the warning:
> CMake Warning at .../zephyr/CMakeLists.txt:2166 (message):
>
> The CMake build type was set to 'MinSizeRel', but the optimization
> flag was set to '-O2'.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>