[Issue 23086] spurious case of `expression has no effect` message

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23086

--- Comment #2 from Basile-z <b2.temp at gmx.com> ---
the check should dig in the sub expressions and take in account if they contain
impure calls, in which case the message should not be emitted.

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