tests: force a utf8 locale because gradle don't like pure ascii
tests: force a utf8 locale because gradle don't like pure ascii

this should fix the CI tests when people with international names make PR.

Signed-off-by: Jean Privat <51f8b1fa9b424745378826727452997ee2a7c3d7@pryen.org>

privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit