[CI] clingtest=ON when cling touched

[ferdymercury]

Explain what you would like to see improved and how.

When a PR touches code within cling subdir, it would be great if the CI turns option clingtest ON automatically.

ROOT version

Any

Installation method

Any

Operating system

Any

Additional context

https://github.com/root-project/root/pull/9272#issuecomment-2053640480 https://github.com/root-project/root/issues/6957 https://github.com/root-project/root/issues/10693