Make DevToolsDataSourceAutoConfiguration back off without DataSource class

Manually tested as an automated test is prohibitively difficult as it
requires hiding one of the JDK's own classes.

Closes gh-40434

Author: wilkinsona

Diff for: spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/autoconfigure/DevToolsDataSourceAutoConfiguration.java

@@ -57,6 +57,7 @@
  * @author Andy Wilkinson
  * @since 1.3.3
  */
+@ConditionalOnClass(DataSource.class)
 @Conditional({ OnEnabledDevToolsCondition.class, DevToolsDataSourceCondition.class })
 @AutoConfiguration(after = DataSourceAutoConfiguration.class)
 @Import(DatabaseShutdownExecutorEntityManagerFactoryDependsOnPostProcessor.class)