Output subprocess stdout if it errored

Signed-off-by: Yuto Takano <yuto.takano@arm.com>
diff --git a/tests/scripts/check-names.py b/tests/scripts/check-names.py
index 8ee5070..3310ae2 100755
--- a/tests/scripts/check-names.py
+++ b/tests/scripts/check-names.py
@@ -513,6 +513,7 @@
                 check=True
             )
         except subprocess.CalledProcessError as error:
+            self.log.debug(error.output)
             self.set_return_code(2)
             raise error
         finally: