test: test_lsblk: Mark as sandbox specific

This test checks for output specific to the sandbox blk device
"sandbox_host_blk", mark it as sandbox specific.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/test/py/tests/test_lsblk.py b/test/py/tests/test_lsblk.py
index 40ffe01..a719a48 100644
--- a/test/py/tests/test_lsblk.py
+++ b/test/py/tests/test_lsblk.py
@@ -4,6 +4,7 @@
 
 import pytest
 
+@pytest.mark.boardspec('sandbox')
 @pytest.mark.buildconfigspec('blk')
 @pytest.mark.buildconfigspec('cmd_lsblk')
 def test_lsblk(u_boot_console):