Avoid using a temporary file to store screenshot after a test failure

Temporary files are created with 600, differing from defined umask.
For the screenshot file that is later attached as diagnostic, this can cause permission issues in some environments.

src/main/java/org/jenkinsci/test/acceptance/junit/DiagnosticRule.java

@@ -1,10 +1,9 @@
 package org.jenkinsci.test.acceptance.junit;
 
 import jakarta.inject.Inject;
-import java.io.File;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.util.logging.Logger;
-import org.apache.commons.io.FileUtils;
 import org.jenkinsci.test.acceptance.controller.JenkinsController;
 import org.jenkinsci.test.acceptance.po.CapybaraPortingLayerImpl;
 import org.junit.rules.TestWatcher;
@@ -44,10 +43,9 @@ protected void failed(Throwable t, Description description) {
 
     private void takeScreenshot() {
         try {
-            File file = diagnostics.touch("screenshot.png");
-            File screenshot = ((TakesScreenshot) driver).getScreenshotAs(OutputType.FILE);
-            FileUtils.copyFile(screenshot, file);
-
+            Files.write(
+                    diagnostics.touch("screenshot.png").toPath(),
+                    ((TakesScreenshot) driver).getScreenshotAs(OutputType.BYTES));
         } catch (IOException e) {
             logger.warning("An error occurred when taking screenshot");
             throw new Error(e);