[LINTER] Exclude a new rule that enforce naming convention on classes

Summary:
The Generic.NamingConventions.AbstractClassNamePrefix is new from
phpcs version 3.6.0 and not consistent with our codebase.

Test Plan:

arc lint --everything

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9611