[ci] remove unused import

Author: hazendaz

src/test/java/org/apache/ibatis/io/ExternalResourcesTest.java

@@ -21,7 +21,6 @@
 import java.io.FileNotFoundException;
 import java.io.FileWriter;
 import java.io.IOException;
-import java.nio.charset.StandardCharsets;
 
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;