Fix erroneous imports in unittests

[RazvanN7]

This is part 2 of #6048 and is currently blocking : dlang/dmd#7760 because deprecations are treated as errors.

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[wilzbach]

Argh - this is needed because the Windows branch is public import core.sys.windows.winsock2;

[wilzbach]

This needs to be import std.experimental.logger.core : LogLevel; instead

[RazvanN7]

The fail in jenkins seems unrelated. @atilaneves does this affect your project?

[atilaneves]

@RazvanN7 I think that's a spurious error that has to do with an stdio bug. I'm confident that if rerun it'll be green.

[RazvanN7]

@atilaneves ok. thanks! can you readd the auto-merge label please?