Expose player_t.muted as read+write

Lugentrequested to merge
Lugent/SRB2:expose-player-muted into next

Exposes player_t.muted to Lua as a read+write field, when Hanicef was making !2259 (merged) he forgot to expose the muted field to Lua. So I noticed that out (late of course xd) and made my way to make this MR.

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