Use inputExcludes instead of the deprecated excludes

[slawekjaranowski]

The excludes parameter of apache-rat-plugin is deprecated for removal
since RAT 0.17. With RAT 0.18, used since maven-plugins 50, the build logs:

[WARNING] Parameter 'excludes' is deprecated: Deprecated for removal
          since 0.17: Use <inputExclude> instead.
[WARNING] Use of deprecated option 'exclude'. Deprecated for removal
          since 0.17: Use <inputExclude> instead.

Switching to inputExcludes clears both warnings. The combine.children="append"
attribute is dropped as well, matching what was already done in
maven-source-plugin, maven-resources-plugin, maven-rar-plugin,
maven-checkstyle-plugin and maven-deploy-plugin.

Verified locally with mvn apache-rat:check - no warnings remain.

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