Allow clash in spring.config.name

Remove the recently added slash restriction since Spring Cloud
Config Server needs to support names with slashes.

See gh-21217

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigFileApplicationListener.java

@@ -728,8 +728,6 @@ public class ConfigFileApplicationListener implements EnvironmentPostProcessor,
 
 		private void assertValidConfigName(String name) {
 			Assert.state(!name.contains("*"), () -> "Config name '" + name + "' cannot contain wildcards");
-			Assert.state(!name.contains("/") && !name.contains("\\"),
-					() -> "Config name '" + name + "' cannot contain slashes");
 		}
 
 		private void addLoadedPropertySources() {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/config/ConfigFileApplicationListenerTests.java

@@ -1051,6 +1051,14 @@ class ConfigFileApplicationListenerTests {
 				.withMessage("Config name '*/application' cannot contain wildcards");
 	}
 
+	@Test
+	void configNameCanContainSlash() {
+		// Spring Cloud config server depends on this
+		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(this.environment,
+				"spring.config.location=file:src/test/resources/", "spring.config.name=config/application");
+		this.initializer.postProcessEnvironment(this.environment, this.application);
+	}
+
 	@Test
 	void directoryLocationsWithMultipleWildcardsShouldThrowException() {
 		String location = "file:src/test/resources/config/**/";