fix: rename test module to tests

examples/acceptance_tests/015/lib/tests.ak

@@ -0,0 +1,11 @@
+pub opaque type Map<key, value> {
+  inner: List<#(key, value)>,
+}
+
+pub fn new() {
+  Map { inner: [] }
+}
+
+test new_1() {
+  new() == Map { inner: [] }
+}