/usr/share/vala/vapi/fsotest-2.0.deps is in libfsoframework-dev 0.12.0-7.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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posix glib-2.0 gio-2.0 gmodule-2.0 fsobasics-2.0