games/veloren: Fix build with rust 1.59.0

error: format argument must be a string literal

--> voxygen/src/hud/diary.rs:1263:49
 |

1263 | unknown => unreachable!(unknown),

|                                                 ^^^^^^^

Upstream PR: https://gitlab.com/veloren/veloren/-/issues/1493

Approved by: portmgr (build fix blanket)