[CI] address cmakelint warnings about whitespace (#9674)

plugin/CMakeLists.txt

@@ -1,8 +1,8 @@
-if (PLUGIN_DENSE_PARSER)
+if(PLUGIN_DENSE_PARSER)
   target_sources(objxgboost PRIVATE ${xgboost_SOURCE_DIR}/plugin/dense_parser/dense_libsvm.cc)
 endif()
 
-if (PLUGIN_UPDATER_ONEAPI)
+if(PLUGIN_UPDATER_ONEAPI)
   add_library(oneapi_plugin OBJECT
     ${xgboost_SOURCE_DIR}/plugin/updater_oneapi/regression_obj_oneapi.cc
     ${xgboost_SOURCE_DIR}/plugin/updater_oneapi/predictor_oneapi.cc)
@@ -18,7 +18,7 @@ if (PLUGIN_UPDATER_ONEAPI)
     CXX_STANDARD 17
     CXX_STANDARD_REQUIRED ON
     POSITION_INDEPENDENT_CODE ON)
-  if (USE_OPENMP)
+  if(USE_OPENMP)
     find_package(OpenMP REQUIRED)
     target_link_libraries(oneapi_plugin PUBLIC OpenMP::OpenMP_CXX)
   endif()
@@ -29,6 +29,6 @@ if (PLUGIN_UPDATER_ONEAPI)
 endif()
 
 # Add the Federate Learning plugin if enabled.
-if (PLUGIN_FEDERATED)
+if(PLUGIN_FEDERATED)
   add_subdirectory(federated)
 endif()