Resolve clippy::single-match-else warnings

- See https://rust-lang.github.io/rust-clippy/master/index.html#single_match_else
- Also avoid introducing a clippy::manual-let-else warning in the process

src/bin/scaffold.rs

@@ -54,12 +54,9 @@ fn create_file(path: &str) -> Result<File, std::io::Error> {
 }
 
 fn main() {
-    let day = match parse_args() {
+    let Ok(day) = parse_args() else {
-        Ok(day) => day,
+        eprintln!("Need to specify a day (as integer). example: `cargo scaffold 7`");
-        Err(_) => {
+        process::exit(1);
-            eprintln!("Need to specify a day (as integer). example: `cargo scaffold 7`");
-            process::exit(1);
-        }
     };
 
     let day_padded = format!("{day:02}");