[REG2.067a] Issue 13300 - pure function 'std.array.Appender!(T[]).Appender.ensureAddable' cannot call impure function 'test.T.__fieldPostBlit'

https://issues.dlang.org/show_bug.cgi?id=13300

This PR requires compiler fix: https://github.com/D-Programming-Language/dmd/pull/3878