tests: fix incorrect --write-junit-xml code
In
78d5e4cfb4b (tests: refactor --write-junit-xml code, 2022-05-21),
this developer refactored the `--write-junit-xml` code a bit, including
the part where the current test case's title was used in a `set`
invocation, but failed to account for the fact that some test cases'
titles start with a long option, which the `set` misinterprets as being
intended for parsing.
Let's fix this by using the `set -- <...>` form.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>