test: Move the non-LTO test to sandbox_flattree

The sandbox build is about to be used for ulib, so will not support LTO.
Use the sandbox_flatree build to check disabling LTO.

There is limited value in this, since sandbox will already check
building without LTO. But it seems reasonable to keep the test working,
making sure that the same board can build with and without LTO.

Signed-off-by: Simon Glass <sjg@chromium.org>

test/py/tests/test_sandbox_opts.py

@@ -19,10 +19,10 @@ def test_sandbox_cmdline(ubman):
                '-a', '~CMDLINE', '-o', TMPDIR])
 
 @pytest.mark.slow
-@pytest.mark.boardspec('sandbox')
+@pytest.mark.boardspec('sandbox_flattree')
 def test_sandbox_lto(ubman):
-    """Test building sandbox without CONFIG_LTO"""
+    """Test building sandbox_flattree without CONFIG_LTO"""
 
     utils.run_and_log(
-        ubman, ['./tools/buildman/buildman', '-m', '--board', 'sandbox',
-               '-a', '~LTO', '-o', TMPDIR])
+        ubman, ['./tools/buildman/buildman', '-m', '--board',
+                'sandbox_flattree', '-a', '~LTO', '-o', TMPDIR])