[CMake] Fix dependency on Git information.

The incorrect (and non-existent) file `include/mutable/version.cpp` was
specified.  It should be `include/mutable/version.hpp` instead, which
`#include`s the generated `gitversion.tbl` file.

Author: ImmanuelHaffner

CMakeLists.txt

@@ -210,7 +210,7 @@ add_custom_command(
 add_custom_target(gitversion ALL DEPENDS "${GITREV_FILE}")
 # Apparently, CMake's dependency scanner does not recognize the dependency to the GITREV_FILE.  We add it manually.
 set_source_files_properties(
-    "${CMAKE_SOURCE_DIR}/include/mutable/version.cpp"
+    "${CMAKE_SOURCE_DIR}/include/mutable/version.hpp"
     PROPERTIES OBJECT_DEPENDS "${GITREV_FILE}"
 )