Fix "Configure Two DataSources" example

With the present example, the `secondDataSource` bean factory method
will use `firstDataSourceProperties` due to it being annotated with
`@Primary`.

This commit adds the `@Qualifier` needed to ensure `secondDataSource`
bean factory method uses `secondDataSourceProperties`.

See gh-28712

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/howto/dataaccess/configuretwodatasources/MyCompleteDataSourcesConfiguration.java

@@ -19,6 +19,7 @@
 import com.zaxxer.hikari.HikariDataSource;
 import org.apache.commons.dbcp2.BasicDataSource;
 
+import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.context.annotation.Bean;
@@ -50,7 +51,8 @@ public DataSourceProperties secondDataSourceProperties() {
 
 	@Bean
 	@ConfigurationProperties("app.datasource.second.configuration")
-	public BasicDataSource secondDataSource(DataSourceProperties secondDataSourceProperties) {
+	public BasicDataSource secondDataSource(
+			@Qualifier("secondDataSourceProperties") DataSourceProperties secondDataSourceProperties) {
 		return secondDataSourceProperties.initializeDataSourceBuilder().type(BasicDataSource.class).build();
 	}