fix: rename test module to tests

examples/acceptance_tests/013/lib/tests.ak

@@ -0,0 +1,13 @@
+pub fn unzip(xs: List<#(a, b)>) -> #(List<a>, List<b>) {
+  when xs is {
+    [] -> #([], [])
+    [#(a, b), ..rest] -> {
+      let #(a_tail, b_tail) = unzip(rest)
+      #([a, ..a_tail], [b, ..b_tail])
+    }
+  }
+}
+
+test unzip_1() {
+  unzip([#(1, "a"), #(2, "b")]) == #([1, 2], ["a", "b"])
+}