Duplicated message for file type check

[ernilambar]

For file .DS_Store, two errors are triggered: hidden_files and application_detected

In this PR, I have removed DS_Store extension from the list of application extensions.

For .DS_Store file, hidden_files error is already triggered. So, I believe application check should not test for DS_Store.

This will fix duplicated message for the same file.

PR also includes scenario in the feature test for the related change.

[github-actions]

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Co-authored-by: ernilambar <rabmalin@git.wordpress.org>
Co-authored-by: swissspidy <swissspidy@git.wordpress.org>
Co-authored-by: davidperezgar <davidperez@git.wordpress.org>

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