fix: rename test module to tests

examples/acceptance_tests/027/lib/tests.ak

@@ -0,0 +1,11 @@
+pub fn foo(_a : a) -> Bool {
+  True
+}
+
+test test_1() {
+  foo(1)
+}
+
+test test_2() {
+  foo(1) && foo(2)
+}