benchmark

Removing warnings appearing with C++20 / CLang 15 (#1542)

* Removing warnings appearing with C++20 / CLang 15

```
[ 70%] Building CXX object _deps/benchmark-build/test/CMakeFiles/benchmark_min_time_flag_time_test.dir/benchmark_min_time_flag_time_test.cc.o
/home/xxx/cpp/_deps/benchmark-src/test/benchmark_min_time_flag_time_test.cc:31:55: warning: unused parameter 'has_explicit_iters' [-Wunused-parameter]
  virtual void ReportRunsConfig(double min_time, bool has_explicit_iters,
                                                      ^
/home/xxx/cpp/_deps/benchmark-src/test/benchmark_min_time_flag_time_test.cc:32:48: warning: unused parameter 'iters' [-Wunused-parameter]
                                IterationCount iters) BENCHMARK_OVERRIDE {
                                               ^
2 warnings generated.
```

```
[ 70%] Building CXX object _deps/benchmark-build/test/CMakeFiles/benchmark_min_time_flag_iters_test.dir/benchmark_min_time_flag_iters_test.cc.o
/home/xxx/cpp/_deps/benchmark-src/test/benchmark_min_time_flag_iters_test.cc:22:36: warning: implicit conversion loses integer precision: 'const benchmark::IterationCount' (aka 'const long') to 'std::vector<int>::value_type' (aka 'int') [-Wshorten-64-to-32]
    iter_nums_.push_back(report[0].iterations);
               ~~~~~~~~~ ~~~~~~~~~~^~~~~~~~~~
1 warning generated.
```

* Refactoring to get the proper type of collection

* Refactoring to get the proper type of collection

* clang format

* bug fix in main