[Issue 18486] std.format cannot format const objects

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18486

--- Comment #3 from github-bugzilla at puremagic.com ---
Commit pushed to master at https://github.com/dlang/phobos

https://github.com/dlang/phobos/commit/93dc74be78de197d8c1daa52d9bd1920d07d7f47
Merge pull request #6207 from JackStouffer/issue18486

Fix Issue 7879 - format of const class with non const toString()

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