Fix spelling errors

Used config files:
    1: .codespellrc

-------8<-------
SUMMARY:
chnages       1
ser           1

publish/src/bin/janitor-publish.rs

@@ -46,7 +46,7 @@ struct Args {
     #[clap(long)]
     slowstart: bool,
 
-    /// Only publish chnages that were reviewed.
+    /// Only publish changes that were reviewed.
     #[clap(long)]
     reviewed_only: bool,
 

publish/src/lib.rs

@@ -6,7 +6,7 @@ use janitor::config::Campaign;
 use janitor::publish::{MergeProposalStatus, Mode};
 use janitor::vcs::{VcsManager, VcsType};
 use reqwest::header::HeaderMap;
-use serde::ser::SerializeStruct;
+use serde::set::SerializeStruct;
 use std::collections::HashMap;
 use std::path::PathBuf;
 use std::sync::{Arc, Mutex, RwLock};