Polish "Validate overrides against CharsetMapperDefault.properties"

See gh-30692

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/tomcat/TomcatServletWebServerFactoryTests.java

@@ -81,6 +81,8 @@ import org.springframework.boot.web.server.WebServerException;
 import org.springframework.boot.web.servlet.server.AbstractServletWebServerFactory;
 import org.springframework.boot.web.servlet.server.AbstractServletWebServerFactoryTests;
 import org.springframework.core.io.ByteArrayResource;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.support.PropertiesLoaderUtils;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
@@ -410,8 +412,8 @@ class TomcatServletWebServerFactoryTests extends AbstractServletWebServerFactory
 		TomcatServletWebServerFactory factory = getFactory();
 		this.webServer = factory.getWebServer();
 		// override defaults, see org.apache.catalina.util.CharsetMapperDefault.properties
-		Properties charsetMapperDefault = new Properties();
-		charsetMapperDefault.load(CharsetMapper.class.getResourceAsStream("CharsetMapperDefault.properties"));
+		Properties charsetMapperDefault = PropertiesLoaderUtils
+				.loadProperties(new ClassPathResource("CharsetMapperDefault.properties", CharsetMapper.class));
 		for (String language : charsetMapperDefault.stringPropertyNames()) {
 			assertThat(getCharset(new Locale(language))).isEqualTo(StandardCharsets.UTF_8);
 		}