Fix allowed_warnings placement in system ingest processor YAML test (#20770)

The v2 index template test had allowed_warnings on the document index
step, but the warning about overlapping template patterns is emitted
during put_index_template for v2 composable templates, not at index
time. Move allowed_warnings to the correct step with the actual warning
message returned by the server.

Signed-off-by: Andrew Ross <andrross@amazon.com>

Author: andrross

plugins/examples/system-ingest-processor/src/yamlRestTest/resources/rest-api-spec/test/example-system-ingest-processor/20_system_ingest_processor.yml

@@ -111,6 +111,8 @@ teardown:
   - skip:
       features: allowed_warnings
   - do:
+      allowed_warnings:
+        - "index template [example-template] has index patterns [template-*] matching patterns from existing older templates [global] with patterns (global => [*]); this template [example-template] will take precedence during new index creation"
       # test v2 template
       indices.put_index_template:
         name: example-template
@@ -120,8 +122,6 @@ teardown:
             settings:
               index.example_system_ingest_processor_plugin.trigger_setting: true
   - do:
-      allowed_warnings:
-        - "index [template-index-1] matches multiple legacy templates [example-template, global], composable templates will only match a single template"
       index:
         index: template-index-1
         id: 1