Resolve uninlined_format_args clippy lint in demo

[dtolnay]

warning: variables can be used directly in the `format!` string
  --> demo/src/main.rs:51:5
   |
51 |     println!("blobid = {}", blobid);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
   = note: `-W clippy::uninlined-format-args` implied by `-W clippy::all`
   = help: to override `-W clippy::all` add `#[allow(clippy::uninlined_format_args)]`
help: change this to
   |
51 -     println!("blobid = {}", blobid);
51 +     println!("blobid = {blobid}");
   |