lit-test: fix inferencer/error_class test (broken in b0c6b70).

lit-test/test/inferencer/error_class.py

@@ -8,9 +8,3 @@ class a(1):
 class b:
     # CHECK-L: ${LINE:+1}: fatal: class body must contain only assignments and function definitions
     x += 1
-
-class c:
-    pass
-# CHECK-L: ${LINE:+1}: fatal: variable 'c' is already defined
-class c:
-    pass

lit-test/test/inferencer/error_class_redefine.py

@@ -0,0 +1,8 @@
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+class c:
+    pass
+# CHECK-L: ${LINE:+1}: fatal: variable 'c' is already defined
+class c:
+    pass