What version of PHPCS are you using?
If you refer this documentation https://...

What version of PHPCS are you using?

If you refer this documentation https://github.com/squizlabs/PHP_CodeSniffer/wiki/Advanced-Usage#ignoring-parts-of-a-file then it says the following:

Note: Selective ignoring of codes/sniffs/categories/standards is only available from PHP_CodeSniffer version 3.2.0 onwards.

If your PHPCS version is lesser than 3.2.0, then excluding specific sniffs might not be done?