net/unison232: isolate self-test from pre-existing $HOME
On the "exp - 121amd64-default-build-as-use" builder, $HOME appears
to be /nonexistent, and this jeopardizes the self-test.
Feed the selftest mktemp -d as its HOME so it doesn't read from,
or pollute, the actual building user's home directory.
Thanks to: pkg-fallout, kevans, rhtoad.
No PORTREVISION bump as this is purely a build-time fix.
Approved by: ports-secteam (blanket, tested one-line fix to unbreak builds in certain configurations)
49ede1522b