Test using an up-to-date version of Postgres

See gh-28296

Author: wilkinsona

spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/testcontainers/DockerImageNames.java

@@ -34,7 +34,7 @@ public final class DockerImageNames {
 
 	private static final String NEO4J_VERSION = "4.0";
 
-	private static final String POSTGRESQL_VERSION = "9.6.21";
+	private static final String POSTGRESQL_VERSION = "14.0";
 
 	private static final String REDIS_VERSION = "4.0.14";