Updated Postgres version in test.

Author: flexable777

src/test/kotlin/no/nav/klage/document/repositories/TestPostgresqlContainer.kt

@@ -6,7 +6,7 @@ class TestPostgresqlContainer private constructor() :
     PostgreSQLContainer<TestPostgresqlContainer?>(IMAGE_VERSION) {
 
     companion object {
-        private const val IMAGE_VERSION = "postgres:12.6"
+        private const val IMAGE_VERSION = "postgres:15.4"
 
         private val CONTAINER: TestPostgresqlContainer = TestPostgresqlContainer()