raft.h: Fix static assert macro when compiling with C++

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (85ec6a0) 74.03% compared to head (3d50a9a) 73.97%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #166 +/- ## ========================================== - Coverage 74.03% 73.97% -0.06% ========================================== Files 52 52 Lines 10356 10356 Branches 2482 2482 ========================================== - Hits 7667 7661 -6 - Misses 1320 1326 +6 Partials 1369 1369 ```

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