Respect custom username/password properties

Fix a bug in `DataSourceInitializationConfiguration` that was stopping
custom username/password properties from being applied.

Fixes gh-26676

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceInitializationConfiguration.java

@@ -64,7 +64,7 @@ class DataSourceInitializationConfiguration {
 
 	private static DataSource determineDataSource(Supplier<DataSource> dataSource, String username, String password) {
 		if (StringUtils.hasText(username) && StringUtils.hasText(password)) {
-			DataSourceBuilder.derivedFrom(dataSource.get()).type(SimpleDriverDataSource.class).username(username)
+			return DataSourceBuilder.derivedFrom(dataSource.get()).type(SimpleDriverDataSource.class).username(username)
 					.password(password).build();
 		}
 		return dataSource.get();

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jdbc/DataSourceInitializationIntegrationTests.java

@@ -198,7 +198,9 @@ class DataSourceInitializationIntegrationTests {
 						"spring.datasource.schema-username:admin", "spring.datasource.schema-password:admin")
 				.run((context) -> {
 					assertThat(context).hasFailed();
-					assertThat(context.getStartupFailure()).isInstanceOf(BeanCreationException.class);
+					assertThat(context.getStartupFailure()).isInstanceOf(BeanCreationException.class)
+							.hasMessageContaining("invalid authorization specification");
+					context.getStartupFailure().printStackTrace();
 				});
 	}
 
@@ -212,7 +214,8 @@ class DataSourceInitializationIntegrationTests {
 						"spring.datasource.data-username:admin", "spring.datasource.data-password:admin")
 				.run((context) -> {
 					assertThat(context).hasFailed();
-					assertThat(context.getStartupFailure()).isInstanceOf(BeanCreationException.class);
+					assertThat(context.getStartupFailure()).isInstanceOf(BeanCreationException.class)
+							.hasMessageContaining("invalid authorization specification");
 				});
 	}