Replace explicit generics with diamond operator

Where possible, explicit generic declarations to use the Java 8 diamond
operator.

See gh-9781

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/autoconfigure/DevToolsDataSourceAutoConfiguration.java

@@ -126,8 +126,7 @@ public class DevToolsDataSourceAutoConfiguration {
 
 			InMemoryDatabase(String urlPrefix, String... driverClassNames) {
 				this.urlPrefix = urlPrefix;
-				this.driverClassNames = new HashSet<String>(
-						Arrays.asList(driverClassNames));
+				this.driverClassNames = new HashSet<>(Arrays.asList(driverClassNames));
 			}
 
 			boolean matches(DataSourceProperties properties) {