Fix off-by-one error in string formatting in Python

Signed-off-by: Yuto Takano <yuto.takano@arm.com>
diff --git a/tests/scripts/check_names.py b/tests/scripts/check_names.py
index 9577014..591389b 100755
--- a/tests/scripts/check_names.py
+++ b/tests/scripts/check_names.py
@@ -138,7 +138,7 @@
     def __str__(self):
         if self.quiet:
             return (
-                "{0}:{1}:{3}"
+                "{0}:{1}:{2}"
                 .format(self.match.filename, self.match.pos[0], self.match.name)
             )