xml-maven-plugin validation should not validate '.ci-temp' folder

[romani]

Build might fail at xml-maven-plugin validation if there is some untracked xml files in repo
in my case it was .ci-temp folder that is leftover from regression execution.

✔ ~/java/github/romani/checkstyle [master L|✔] 
$ ./.ci/pitest.sh pitest-common-2
[INFO] Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO] Inspecting build with total of 1 modules...
[INFO] Installing Nexus Staging features:
[INFO]   ... total of 1 executions of maven-deploy-plugin replaced with nexus-staging-maven-plugin
[INFO] 
[INFO] ------------------< com.puppycrawl.tools:checkstyle >-------------------
[INFO] Building checkstyle 8.36-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
......
[INFO] 
[INFO] --- xml-maven-plugin:1.0.2:check-format (default) @ checkstyle ---
[ERROR] /home/rivanov/java/github/romani/checkstyle/./.ci-temp/checks-only-javadoc-error.xml:14,70:
 Delete 2 spaces. Expected 4 found 6 spaces before start element <property>
[ERROR] /home/rivanov/java/github/romani/checkstyle/./.ci-temp/trunk/native/linux/
latest/usr/share/mime/packages/josm-latest.xml:3,49: 
Delete 6 spaces. Expected 2 found 8 spaces before start element <mime-type>
....

[pbludov]

Fix is merged