[clang-tidy] Fixed abseil-duration-unnecessary-conversion tests for c++17

Summary: Fixed abseil-duration-unnecessary-conversion tests for c++17

Reviewers: hokein, gribozavr

Reviewed By: gribozavr

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D63263

Patch by Johan Vikström.

llvm-svn: 363263