[JohanLorenzo]

Replace four empty-value assertions with equality assertions so Clippy 1.99.0 passes with pedantic warnings denied. Found in https://github.com/mozilla/stmo-cli/actions/runs/36969585007/job/110720550646?pr=54:

error: used `assert!` to check that a value is empty
   --> src/commands/dashboards.rs:565:9
    |
565 |         assert!(slugs.is_empty());
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.99.0/index.html#assert_is_empty
    = note: `-D clippy::assert-is-empty` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::assert_is_empty)]`
help: use `assert_eq!` to show the value on failure
    |
565 -         assert!(slugs.is_empty());
565 +         assert_eq!(slugs, [] as [std::string::String; 0]);
    |

error: used `assert!` to check that a value is empty
   --> src/commands/snippets.rs:449:9
    |
449 |         assert!(result.unwrap().is_empty());
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.99.0/index.html#assert_is_empty
help: use `assert_eq!` to show the value on failure
    |
449 -         assert!(result.unwrap().is_empty());
449 +         assert_eq!(result.unwrap(), [] as [u64; 0]);
    |

error: used `assert!` to check that a value is empty
   --> src/commands/snippets.rs:458:9
    |
458 |         assert!(result.unwrap().is_empty());
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.99.0/index.html#assert_is_empty
help: use `assert_eq!` to show the value on failure
    |
458 -         assert!(result.unwrap().is_empty());
458 +         assert_eq!(result.unwrap(), [] as [u64; 0]);
    |

error: used `assert!` to check that a value is empty
   --> src/commands/snippets.rs:678:9
    |
678 |         assert!(metadata.is_empty());
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.99.0/index.html#assert_is_empty
help: use `assert_eq!` to show the value on failure
    |
678 -         assert!(metadata.is_empty());
678 +         assert_eq!(metadata, [] as [(u64, std::string::String); 0]);
    |

error: could not compile `stmo-cli` (lib test) due to 4 previous errors
warning: build failed, waiting for other jobs to finish...
error: could not compile `stmo-cli` (bin "stmo-cli" test) due to 4 previous errors
Error: Process completed with exit code 101.