vfmt: change all '$expr' to '${expr}' (#16428)

examples/concurrency/concurrency.v

@@ -2,9 +2,9 @@ import time
 
 // Simulate expensive computing using sleep function
 fn expensive_computing(id int, duration int) {
-	println('Executing expensive computing task ($id)...')
+	println('Executing expensive computing task (${id})...')
 	time.sleep(duration * time.millisecond)
-	println('Finish task $id on $duration ms')
+	println('Finish task ${id} on ${duration} ms')
 }
 
 fn main() {

examples/concurrency/concurrency_returns.v

@@ -9,5 +9,5 @@ fn main() {
 	}
 	// Join all tasks
 	r := threads.wait()
-	println('All jobs finished: $r')
+	println('All jobs finished: ${r}')
 }