Use consistent exception messages in Assert calls

Update `Assert` calls to consistently use messages of the form
"'item' must [not] ...".

Closes gh-43780

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/FilterableDependency.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -79,7 +79,7 @@ public abstract class FilterableDependency {
 	public void set(String property) {
 		String[] parts = property.split(":");
 		Assert.isTrue(parts.length == 2 || parts.length == 3, getClass().getSimpleName()
-				+ " must be in the form groupId:artifactId or groupId:artifactId:classifier");
+				+ " 'property' must be in the form groupId:artifactId or groupId:artifactId:classifier");
 		setGroupId(parts[0]);
 		setArtifactId(parts[1]);
 		if (parts.length == 3) {