tests: Add test for break in for.

For #635 / 25c84643b6.

tests/basics/for_break.py

@@ -0,0 +1,15 @@
+# Testcase for break in a for [within bunch of other code]
+# https://github.com/micropython/micropython/issues/635
+
+def foo():
+    seq = [1, 2, 3]
+    v = 100
+    i = 5
+    while i > 0:
+        print(i)
+        for a in seq:
+            if a == 2:
+                break
+        i -= 1
+
+foo()