Prevent major version upgrades in docker-compose/elasticsearch/v6/doc…

…ker-compose.yml (#5710)

renovate bot tried to bump it to v7

---------

Signed-off-by: Mend Renovate <bot@renovateapp.com>
Signed-off-by: Yuri Shkuro <github@ysh.us>
Co-authored-by: Yuri Shkuro <github@ysh.us>

renovate.json

@@ -17,6 +17,7 @@
       "matchFileNames": [
         "docker-compose/cassandra/v3/docker-compose.yaml",
         "docker-compose/cassandra/v4/docker-compose.yaml",
+        "docker-compose/elasticsearch/v6/docker-compose.yml",
         "docker-compose/elasticsearch/v7/docker-compose.yml",
         "docker-compose/elasticsearch/v8/docker-compose.yml",
         "docker-compose/kafka-integration-test/docker-compose.yml",