Upgrade clang-tidy on CI. (#5469)

* Correct all clang-tidy errors.
* Upgrade clang-tidy to 10 on CI.

Co-authored-by: Hyunsu Cho <chohyu01@cs.washington.edu>

tests/cpp/common/test_group_data.cc

@@ -8,7 +8,7 @@
 namespace xgboost {
 namespace common {
 
-TEST(group_data, ParallelGroupBuilder) {
+TEST(GroupData, ParallelGroupBuilder) {
   std::vector<size_t> offsets;
   std::vector<Entry> data;
   ParallelGroupBuilder<Entry, size_t> builder(&offsets, &data);