Update DScanner to 6ba40537532fd795e83db0a7c8609512decdefc5

[wilzbach]

See also:

• Make visiting alias public dlang-community/D-Scanner#549 fix for DScanner
• Merge remote-tracking branch 'upstream/master' into merge_master dlang-community/D-Scanner#550 (update PR for the phobos branch)
• Fix Issue 18243 - selective import + overload = private visibility dmd#7766 (compiler fix + origin of the failures)

[dlang-bot]

Thanks for your pull request, @wilzbach!

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[wilzbach]

This fixes the CircleCi failure.

(FWIW we currently still allow failures for D-Scanner as we still haven't fixed the segfault in druntime GC collection, see e.g. #5929)