When SE-0412 (strict concurrency for global variables) is enabled, each
global or static mutable variable will be diagnosed if it isn't
explicitly on a global actor or `nonisolated(unsafe)`.
Suppress diagnostics for references to such global variables when they
are in the same module as the declaration of the global variable
itself. While these diagnostics are technically correct, they are not
strictly necessary since we've already diagnosed the global variable
itself (with more actionable advice), and they tend to pile on the
developer in a manner that is not helpful.
