bug#63310: 29.0.90; Blacklisting docstrings and docstrings-non-ascii-quotes from byte-compile-warnings do not prevent all docstring warnings

[Jimmy Yuen Ho Wong]

Reproduction:

1. `(custom-set-variables '(byte-compile-warnings '(not docstrings
docstrings-non-ascii-quotes)))`
2. M-x package-install RET move-dup
3. M-x package-install RET monky
4. Observe in the *Compile-Log* buffer the `custom-declare-variable
... docstring has wrong usage of unescaped single quotes (use \= or different 
quoting)` and `docstring wider than ... characters` mesages

Expectation:

Blacklisting docstrings and docstrings-non-ascii-quotes should not result
in any docstring warnings being emitted during byte compilation.