Fix test bug when testing the merging of mappings and templates. (#38021)

This test performs a typed index call when it actually means to run a typeless
index call.

Author: jpountz

rest-api-spec/src/main/resources/rest-api-spec/test/indices.create/20_mix_typeless_typeful.yml

@@ -123,7 +123,6 @@
  - do:
       index:
           index: test-1
-          type: my_type
           body: { bar: 42 }
 
  - do: