tests/run-tests: Allow to skip set tests.

If sets are not enabled, set literals lead to SyntaxError during parsing,
so it requires feature_check. Set tests are skipped based on set_*.py
pattern.

tests/basics/set_basic.py

@@ -0,0 +1,17 @@
+# basic sets
+
+s = {1}
+print(s)
+
+s = {3, 4, 3, 1}
+print(sorted(s))
+
+# expression in constructor
+s = {1 + len(s)}
+print(s)
+
+# Sets are not hashable
+try:
+    {s: 1}
+except TypeError:
+    print("TypeError")