add note about disable_logging

Fixes #34037

Author: IanButterworth

base/logging/logging.jl

@@ -543,7 +543,8 @@ with_logstate(f::Function, logstate) = @with(CURRENT_LOGSTATE => logstate, f())
 
 Disable all log messages at log levels equal to or less than `level`.  This is
 a *global* setting, intended to make debug logging extremely cheap when
-disabled.
+disabled. Note that this cannot be used to enable logging that is currently disabled
+by other mechanisms.
 
 # Examples
 ```julia