chore: fix compiler warnings

src/configure.rs

@@ -318,7 +318,7 @@ async fn configure(ctx: &Context, param: &mut LoginParam) -> Result<()> {
     }
 
     // respect certificate setting from function parameters
-    for mut server in &mut servers {
+    for server in &mut servers {
         let certificate_checks = match server.protocol {
             Protocol::Imap => param.imap.certificate_checks,
             Protocol::Smtp => param.smtp.certificate_checks,

src/mimeparser.rs

@@ -643,7 +643,7 @@ impl MimeMessage {
                     .parts
                     .iter_mut()
                     .find(|part| !part.msg.is_empty() && !part.is_reaction);
-                if let Some(mut part) = part_with_text {
+                if let Some(part) = part_with_text {
                     part.msg = format!("{} – {}", subject, part.msg);
                 }
             }