Use Python 3.5 style typing for dependencies

Signed-off-by: Werner Lewis <werner.lewis@arm.com>
diff --git a/scripts/mbedtls_dev/test_generation.py b/scripts/mbedtls_dev/test_generation.py
index 9eaa7e2..1adf8e2 100644
--- a/scripts/mbedtls_dev/test_generation.py
+++ b/scripts/mbedtls_dev/test_generation.py
@@ -52,7 +52,7 @@
     """
     count = 0
     case_description = ""
-    dependencies: List[str] = []
+    dependencies = [] # type: List[str]
     target_basename = ""
     test_function = ""
     test_name = ""