tests/heapalloc_int_from_bytes: Test that int.from_bytes() can work w/o alloc.

For a small number of bytes, it's expected to return a small int without
allocation.

tests/micropython/heapalloc_int_from_bytes.py

+# Test that int.from_bytes() for small number of bytes generates
+# small int.
+import micropython
+
+micropython.heap_lock()
+print(int.from_bytes(b"1", "little"))
+print(int.from_bytes(b"12", "little"))
+micropython.heap_unlock()

tests/micropython/heapalloc_int_from_bytes.py.exp

+49
+12849