Explicitly cast int literals to int8_t in tests to silence implicit-conversion warnings (#1455)
Explicitly cast int literals to int8_t in tests to silence implicit-conversion warnings (#1455)

* Explicitly cast int literals to int8_t in tests so silence implicit-conversion warnings

Error came from:
```
: error: implicit conversion loses integer precision: 'const int' to 'const signed char' [-Werror,-Wimplicit-int-conversion]
```

* clang format

* undo deleted line
google/benchmark,google/benchmark,google/benchmark