[CI] Updates bumpmatrix automation for main

Author: picandocodigo

rake_tasks/automation.rake

@@ -107,11 +107,16 @@ namespace :automation do
       if file == '.buildkite/pipeline.yml'
         require 'yaml'
         yaml = YAML.safe_load(content)
-        branch = version.match(/([0-9]+\.[0-9]+)\.[0-9]+.*/)[1]
         yaml_tests_branch = yaml['steps'][0]['env']['ES_YAML_TESTS_BRANCH']
-        next if yaml_tests_branch == 'main'
 
-        content.gsub!(yaml_tests_branch, branch)
+        if yaml_tests_branch == 'main'
+          old = content.match(/STACK_VERSION: (.*)/)[1]
+          new = "STACK_VERSION: #{version}"
+          content.gsub!(new, old)
+        else
+          branch = version.match(/([0-9]+\.[0-9]+)\.[0-9]+.*/)[1]
+          content.gsub!(yaml_tests_branch, branch)
+        end
         puts "[#{yaml_tests_branch}] -> [#{branch}] in #{file.gsub('./', '')}"
       end
       match = content.match(regexp)