[Issue 21774] "formatException is not constant" instead of "static assert error"

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21774

--- Comment #2 from Berni44 <bugzilla at bernis-buecher.de> ---
https://github.com/dlang/phobos/pull/8070 fixed this too.

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