tests/misc: Improve test coverage of py/profile.c.

Signed-off-by: Jeff Epler <jepler@gmail.com>

tests/misc/sys_settrace_cov.py

@@ -0,0 +1,23 @@
+import sys
+
+try:
+    sys.settrace
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
+
+def trace_tick_handler(frame, event, arg):
+    print("FRAME", frame)
+    print("LASTI", frame.f_lasti)
+    return None
+
+
+def f():
+    x = 3
+    return x
+
+
+sys.settrace(trace_tick_handler)
+f()
+sys.settrace(None)