Fix spurious admin dashboard warning when using ElasticSearch 7.x (#23064)

Some 7.x ElasticSearch versions support some 6.x nodes, thus the version check
is inadequate. I am not sure there is a good way to check if a server
implements all the 7.x APIs, so check server version and minimum wire version
instead.

app/lib/admin/system_check/elasticsearch_check.rb

@@ -30,19 +30,24 @@ class Admin::SystemCheck::ElasticsearchCheck < Admin::SystemCheck::BaseCheck
 
   def running_version
     @running_version ||= begin
-      Chewy.client.info['version']['minimum_wire_compatibility_version'] ||
-        Chewy.client.info['version']['number']
+      Chewy.client.info['version']['number']
     rescue Faraday::ConnectionFailed
       nil
     end
   end
 
+  def compatible_wire_version
+    Chewy.client.info['version']['minimum_wire_compatibility_version']
+  end
+
   def required_version
     '7.x'
   end
 
   def compatible_version?
     return false if running_version.nil?
-    Gem::Version.new(running_version) >= Gem::Version.new(required_version)
+
+    Gem::Version.new(running_version) >= Gem::Version.new(required_version) ||
+      Gem::Version.new(compatible_wire_version) >= Gem::Version.new(required_version)
   end
 end