truncate file on test

lab3/zad2/src/main.rs

@@ -78,7 +78,7 @@ fn main() -> io::Result<()> {
 
     let mut results_file = OpenOptions::new()
         .create(true)
-        .append(true)
+        .truncate(true)
         .open(format!("./results/k1"))?;
 
     for n in (100..=50000).step_by(100) {