lint: Silence a clippy::single_match warning

This warning is documented as being just for "readability" via making
the body less nested:
  https://rust-lang.github.io/rust-clippy/master/index.html#single_match

But here, we have several neighboring matches on the same structure
which can't be simplified this way.  It's better to keep this bit
parallel to those, rather than to simplify it in isolation.

src/main.rs

@@ -149,6 +149,7 @@ fn set(path: PathBuf, query: &str, value_str: &str) -> Result<(), Error> {
                 if n >= &len {
                     Err(CliError::ArrayIndexOob())?;
                 }
+                #[allow(clippy::single_match)]
                 match &item { Item::Value(_) => already_inline = true, _ => () };
                 item = &mut item[n];
             }