feat: Add Config::FixIsChatmail

Add a config option preventing autoconfiguring `IsChatmail` for tests.

src/scheduler.rs

@@ -466,11 +466,13 @@ pub async fn convert_folder_meaning(
 }
 
 async fn inbox_fetch_idle(ctx: &Context, imap: &mut Imap, mut session: Session) -> Result<Session> {
-    ctx.set_config_internal(
-        Config::IsChatmail,
-        crate::config::from_bool(session.is_chatmail()),
-    )
-    .await?;
+    if !ctx.get_config_bool(Config::FixIsChatmail).await? {
+        ctx.set_config_internal(
+            Config::IsChatmail,
+            crate::config::from_bool(session.is_chatmail()),
+        )
+        .await?;
+    }
 
     // Update quota no more than once a minute.
     if ctx.quota_needs_update(60).await {