Add citus upgrade version for pg15

Author: eaydingol

circleci/images/Makefile

@@ -18,6 +18,8 @@ STYLE_CHECKER_TOOLS_VERSION=0.8.33
 
 # Upgrade tests for the PG major versions from PG_VERSIONS file
 CITUS_UPGRADE_PG_VERSIONS=$(shell head PG_VERSIONS|cut -c 6-|tr '\n' ' ')
+# latest minor version of Citus 12
+CITUS_UPGRADE_VERSIONS_15=v12.1.10
 # 12.1.10 is the latest release of Citus 12 when the test is expanded to cover Citus 12
 CITUS_UPGRADE_VERSIONS_16=v12.1.10
 # Latest minor version of Citus 13