Use Locale.ROOT consistently for toLower/toUpperCase

Closes gh-33708

spring-test/src/main/java/org/springframework/test/context/junit/jupiter/AbstractExpressionEvaluatingCondition.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.test.context.junit.jupiter;
 
 import java.lang.annotation.Annotation;
 import java.lang.reflect.AnnotatedElement;
+import java.util.Locale;
 import java.util.Optional;
 import java.util.function.Function;
 
@@ -192,7 +193,7 @@ abstract class AbstractExpressionEvaluatingCondition implements ExecutionConditi
 			return b;
 		}
 		else if (result instanceof String str) {
-			str = str.trim().toLowerCase();
+			str = str.trim().toLowerCase(Locale.ROOT);
 			if ("true".equals(str)) {
 				return true;
 			}