New CI for DiffTool.java

[relentless-pursuit]

Resolves #186

[romani]

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[romani]

continuation of #192 (comment)

try:

    url: file:///home/runner/work/test-configs
    reference: main

as it most likely neded folder with ".github"

[relentless-pursuit]

done, waiting for CI

[romani]

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[romani]

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[romani]

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[romani]

https://github.com/checkstyle/test-configs/actions/runs/11196866258/job/31126176975?pr=192#step:12:342

[main] INFO com.github.checkstyle.difftool.DiffTool - Testing Checkstyle started
[main] INFO com.github.checkstyle.difftool.DiffTool - Cloning git repository 'diff-java-tool' to repositories/diff-java-tool folder ...
Cloning into 'repositories/diff-java-tool'...
hint: Using 'master' as the name for the initial branch. This default branch name
hint: is subject to change. To configure the initial branch name to use in all
hint: of your new repositories, which will suppress this warning, call:
hint:
hint: 	git config --global init.defaultBranch <name>
hint:
hint: Names commonly chosen instead of 'master' are 'main', 'trunk' and
hint: 'development'. The just-created branch can be renamed via this command:
hint:
hint: 	git branch -m <name>
Note: switching to 'dd6eae8136fd7c8c29127471bf5b94d95a2a0f53'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

[main] INFO com.github.checkstyle.difftool.DiffTool - Cloning git repository 'diff-java-tool' - completed

[main] INFO com.github.checkstyle.difftool.DiffTool - Running command: git fetch origin main:main
fatal: couldn't find remote ref main
Error: Exception in thread "main" com.github.checkstyle.difftool.DiffTool$CommandExecutionException: Command execution failed (Exit code: 128)
	at com.github.checkstyle.difftool.DiffTool.executeCmd(DiffTool.java:1796)
	at com.github.checkstyle.difftool.DiffTool.fetchAdditionalData(DiffTool.java:966)
	at com.github.checkstyle.difftool.DiffTool.cloneRepository(DiffTool.java:879)
	at com.github.checkstyle.difftool.DiffTool.generateCheckstyleReport(DiffTool.java:626)
	at com.github.checkstyle.difftool.DiffTool.launchCheckstyleReport(DiffTool.java:562)
	at com.github.checkstyle.difftool.DiffTool.main(DiffTool.java:132)
Error: Process completed with exit code 1.