fix: Set default data source as ops for release info dashboard

Currently, the release information dashboard data source defaults to mimir-gprd, but release metrics are sent to mimir-ops, so this is a quick fix for that.

Snapshot (24 hrs): https://dashboards.gitlab.net/dashboard/snapshot/xbh9CWOUDNJwaWMNQTAonclWmcue4xUT?orgId=1

$ ./test-dashboard.sh delivery/release_info.dashboard.jsonnet
Installed https://dashboards.gitlab.net/dashboard/snapshot/xbh9CWOUDNJwaWMNQTAonclWmcue4xUT?var-environment=gprd&orgId=1&var-PROMETHEUS_DS=mimir-gitlab-gprd&var-stage=main - delivery: Release Information
# remove the `?var-environment=gprd&orgId=1&var-PROMETHEUS_DS=mimir-gitlab-gprd&var-stage=main` part