Rename FMT_VERSION to FMT_MIN_VERSION in config.cmake template

Context

For some reason the fmt version was rename form FMT_VERSION to FMT_MIN_VERSION, but the cmake template was not updated accordingly.

This should fix issues such as aidge_backend_cpu#10 (closed)

aidge_core-config.cmake.in

 @PACKAGE_INIT@
 
 include(CMakeFindDependencyMacro)
-find_dependency(fmt @FMT_VERSION@)
+find_dependency(fmt @FMT_MIN_VERSION@)
 find_dependency(Threads)
 set(AIDGE_REQUIRES_PYTHON @AIDGE_REQUIRES_PYTHON@)
 set(AIDGE_PYTHON_HAS_EMBED @AIDGE_PYTHON_HAS_EMBED@)