annotate-tests: quote variable expansions containing path names

The test case added by 9466e3809d ("blame: enable funcname blaming with
userdiff driver", 2020-11-01) forgot to quote variable expansions. This
causes failures when the current directory contains blanks.

One variable that the test case introduces will not have IFS characters
and could remain without quotes, but let's quote all expansions for
consistency, not just the one that has the path name.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Acked-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>