cmake: use upstream BoostConfig.cmake unconditionally

Fixes the following deprecation warning:
```
CMake Warning (dev) at src/CMakeLists.txt:38 (find_package):
  Policy CMP0167 is not set: The FindBoost module is removed.  Run "cmake
  --help-policy CMP0167" for policy details.  Use the cmake_policy command to
  set the policy and suppress this warning.
```

Author: lzaoral

src/CMakeLists.txt

@@ -35,7 +35,8 @@ if(SANITIZERS)
 endif()
 
 # find Boost
-find_package(Boost REQUIRED
+set(Boost_VERBOSE TRUE)
+find_package(Boost CONFIG REQUIRED
     COMPONENTS filesystem
                program_options
                regex
@@ -126,7 +127,7 @@ macro(build_pycsdiff version)
 
     # find boost_python${version}
     set(PYTHON_VERSION_SUFFIX "${version}${Python${version}_VERSION_MINOR}")
-    find_package(Boost REQUIRED COMPONENTS python${PYTHON_VERSION_SUFFIX})
+    find_package(Boost CONFIG REQUIRED COMPONENTS python${PYTHON_VERSION_SUFFIX})
     message(STATUS "Python ${version} binding enabled. "
         "The pycsdiff module will be built!")