Infrastructure: Move Depednabot updates weekly

[nschonni]

Removes the limit of 10, so some safe dependencies get PRs and
don't get stuck behind a list of 10 that might be harder to land.
Changes to a weekly schedule to at least there should be less
churn with the removed cap.

[nschonni]

Miss-read the docs originally https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/configuration-options-for-dependency-updates#open-pull-requests-limit so changed it to 99 rather than removing the line