Confirm effectiveness of vuln scans (#2248)

### Time to review: __1 mins__

## Changes proposed

Confirms that grype is scanning down to "medium" level vulnerabilities

## Context for reviewers

I wasn't sure that it was already doing this, and this PR confirms that
it is.

.github/workflows/vulnerability-scans.yml

@@ -147,6 +147,8 @@ jobs:
         with:
           image: ${{ needs.build-and-cache.outputs.image }}
           output-format: table
+          fail-build: true
+          severity-cutoff: medium
 
       - name: Save output to workflow summary
         if: always() # Runs even if there is a failure

.grype.yml

@@ -1,3 +1,5 @@
+fail-on-severity: "medium"
+
 # List of vulnerabilities to ignore for the anchore scan
 # https://github.com/anchore/grype#specifying-matches-to-ignore
 # More info can be found in the docs/infra/vulnerability-management.md file