add test for exceptions with incompatible format

#include "gmock/gmock.h"

#include "fmt/format.h"

#include <string>

#include <exception>

using namespace LAMMPS_NS;

using ::testing::Eq;

    auto text = fmt::format("word {}",val);

    ASSERT_THAT(text, Eq("word -1.5"));

}

TEST(Fmtlib, int_for_double) {

    const double val = -1.5;

    ASSERT_THROW(fmt::format("word {:d}",val),std::exception);

}

TEST(Fmtlib, double_for_int) {

    const int val = 15;

    ASSERT_THROW(fmt::format("word {:g}",val),std::exception);

}