Silence harmless version warning for users that have tagged TF-M.
TF-M creates a very noisy warning when you tag it:
CMake Warning at cmake/version.cmake:28 (message):
Actual TF-M version is not available from Git repository. Settled to
v2.0.0
Call Stack (most recent call first):
CMakeLists.txt:22 (include)
Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
