Polish "Allow overriding image.cleanCache from the command-line"

See gh-32719

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

@@ -102,7 +102,7 @@ public class Image {
 	 * If the cache should be cleaned before building.
 	 * @return {@code true} if the cache should be cleaned
 	 */
-	public Boolean isCleanCache() {
+	public Boolean getCleanCache() {
 		return this.cleanCache;
 	}