Sort tests when generating cases

Signed-off-by: Werner Lewis <werner.lewis@arm.com>
diff --git a/tests/scripts/generate_bignum_tests.py b/tests/scripts/generate_bignum_tests.py
index e8db99d..76bce5e 100755
--- a/tests/scripts/generate_bignum_tests.py
+++ b/tests/scripts/generate_bignum_tests.py
@@ -82,7 +82,7 @@
     @classmethod
     def generate_tests(cls):
         """Generate test cases for the target subclasses."""
-        for subclass in cls.__subclasses__():
+        for subclass in sorted(cls.__subclasses__(), key=lambda c: c.__name__):
             yield from subclass.generate_tests()