[reference model] Fix dim test generation

In tosa_test_gen.py, change output_shape for dim operators to [] instead of [1]

Signed-off-by: Tai Ly <tai.ly@arm.com>
Change-Id: I8e7901e02831e9a467bce17e55e9379cb5f1b739
diff --git a/verif/generator/tosa_test_gen.py b/verif/generator/tosa_test_gen.py
index 8c18e67..3014c81 100644
--- a/verif/generator/tosa_test_gen.py
+++ b/verif/generator/tosa_test_gen.py
@@ -4732,7 +4732,7 @@
 
     @staticmethod
     def dimOp(ser, rng, a, axis, error_name=None):
-        output_shape = [1]
+        output_shape = []
 
         if error_name == ErrorIf.WrongOutputType:
             all_dtypes = [