Clarify how Container's Docker image name is used to name a connection

Closes gh-41111

Author: wilkinsona

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/testing.adoc

@@ -1040,7 +1040,8 @@ For example, a `PostgreSQLContainer` will create both `JdbcConnectionDetails` an
 If you want to create only a subset of the applicable types, you can use the `type` attribute of `@ServiceConnection`.
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-By default `Container.getDockerImageName()` is used to obtain the name used to find connection details.
+By default `Container.getDockerImageName().getRepository()` is used to obtain the name used to find connection details.
+The repository portion of the Docker image name ignores any registry and the version.
 This works as long as Spring Boot is able to get the instance of the `Container`, which is the case when using a `static` field like in the example above.
 
 If you're using a `@Bean` method, Spring Boot won't call the bean method to get the Docker image name, because this would cause eager initialization issues.