Use unique testRestTemplate bean name

Update `SpringBootTestContextCustomizer` to use the full qualified
TestRestTemplate as the registered bean name. Prior to this commit it
was possible that the customizer would replace the relatively common
bean name `testRestTemplate`.

Fixes gh-7711

spring-boot-test/src/main/java/org/springframework/boot/test/context/SpringBootTestContextCustomizer.java

@@ -62,7 +62,7 @@ class SpringBootTestContextCustomizer implements ContextCustomizer {
 
 	private void registerTestRestTemplate(ConfigurableApplicationContext context,
 			BeanDefinitionRegistry registry) {
-		registry.registerBeanDefinition("testRestTemplate",
+		registry.registerBeanDefinition(TestRestTemplate.class.getName(),
 				new RootBeanDefinition(TestRestTemplateFactory.class));
 	}