tf-m-nightly-code-coverage: Set days to keep to 90 for the weekly job

Since the job was switched to be weekly, it makes sense to extend its
retention period in days, otherwise there're very few builds to check
in case of any questions.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I4783f0189c39877936cca08eca358f4070eff186
1 file changed