Fix IT isolation for MNG-6256 IT (#11395) (#11396)

This IT was still "escaping", as Verifier was created for directory below invocation (redirected with -f) option.

Turned this IT into "manually managing" and added `.mvn` to it.

Backport of a46b0c7

Author: cstamas

its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng6256SpecialCharsAlternatePOMLocation.java

@@ -26,6 +26,8 @@
  * This is a test set for <a href="https://issues.apache.org/jira/browse/MNG-6256">MNG-6256</a>: check that directories
  * passed via <code>-f/--file</code> containing special characters do not break the script. E.g
  * <code>-f "directoryWithClosing)Bracket/pom.xml"</code>.
+ *
+ * This IT manually manages {@code .mvn} directories, so instructs Verifier to NOT create any.
  */
 public class MavenITmng6256SpecialCharsAlternatePOMLocation extends AbstractMavenIntegrationTestCase {
     public MavenITmng6256SpecialCharsAlternatePOMLocation() {
@@ -68,7 +70,7 @@ private void runCoreExtensionWithOption(String option, String subDir) throws Exc
         File testDir = new File(resourceDir, "../mng-6256-" + subDir);
         testDir.mkdir();
 
-        Verifier verifier = newVerifier(testDir.getAbsolutePath());
+        Verifier verifier = newVerifier(testDir.getAbsolutePath(), false);
         verifier.addCliArgument(option); // -f/--file
         verifier.addCliArgument("\"" + new File(resourceDir, subDir).getAbsolutePath() + "\""); // "<path>"
         verifier.addCliArgument("validate");