More consistent MQTT error messages

src/mqtt/request/sections.rs

@@ -11,7 +11,7 @@ pub struct SectionId(pub crate::model::SectionId);
 impl SectionId {
     fn get_section(self, sections: &Sections) -> Result<SectionRef, RequestError> {
         sections.get(&self.0).cloned().ok_or_else(|| {
-            RequestError::with_name(ErrorCode::NoSuchSection, "section not found", "section")
+            RequestError::with_name(ErrorCode::NoSuchSection, "no such section", "section")
         })
     }
 }
@@ -114,7 +114,7 @@ impl IRequest for CancelSectionRunIdRequest {
             } else {
                 Err(RequestError::with_name(
                     ErrorCode::NoSuchSectionRun,
-                    "section run does not exist",
+                    "no such section run",
                     "section run",
                 ))
             }