specify the type when constructing unordered_set from iterator
Summary:
Fix a MacOS CI build failure
work/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/usr/include/c++/v1/unordered_set:443:9: note: candidate template ignored: couldn't infer template argument '_Value' [11:46:20] [Step 1/1] unordered_set(_InputIterator __first, _InputIterator __last);
Test Plan: @bot build-osx
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D10990