2.1.18 did not have this problem, and the tests completed successfully within
the sandboxed Homebrew build environment.
With 2.1.19, ssh-import.scm fails unless I build with --no-sandbox. If this
cannot be resolved, I will have to disable "make check" since all builds must be
sandboxed in homebrew/core.
I believe the failure is
Executing: '/usr/bin/ssh-add' '-l' '-E' 'md5' error fetching identities for protocol 1: agent refused operation error fetching identities for protocol 2: agent refused operation
Full log is here: https://gist.github.com/ilovezfs/b10da795bc4a7315233b23cfafabdcd9
(Note that I have run "make install" before "make check" in order to avoid the
failure in T2979.)