Fix dependency review workflow

[cartermckinnon]

What type of PR is this?

What this PR does / why we need it:

Trying to fix the dependency review workflow, which is misconfigured for push and workflow_dispatch events.

Also adds a status badge for this workflow to the README, and removes the "contributions welcome" bade, which I think is clutter. Also fixes the href for the go report card to link to the actual report, not the status badge.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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[k8s-ci-robot]

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