Add regression test for inheritance crash

Amp-Thread-ID: https://ampcode.com/threads/T-3ff237da-1bb4-43d1-abb5-989b228d9f59

Author: jupblb

test/scip/testdata/inheritance.rb

@@ -47,3 +47,7 @@ def write_f_plus_1(a)
   end
 end
 
+Z5 = Object
+class Z6 < Z5
+end
+

test/scip/testdata/inheritance.snapshot.rb

@@ -89,3 +89,12 @@ def write_f_plus_1(a)
    end
  end
 
+ Z5 = Object
+#^^ definition [..] Z5.
+#relation reference=[..] Object#
+#^^^^^^^^^^^ reference [..] Z5.
+#     ^^^^^^ reference [..] Object#
+ class Z6 < Z5
+#      ^^ definition [..] Z6#
+ end
+