fix: rename test module to tests

examples/acceptance_tests/031/lib/tests.ak

@@ -0,0 +1,13 @@
+pub fn clamp(n: Int, min min: Int, max max: Int) -> Int {
+  if n < min {
+    min
+  } else if n > max {
+    max
+  } else {
+    n
+  }
+}
+
+test clamp_1() {
+  clamp(14, min: 0, max: 10) == 10
+}