Integrate GitHub security dismissed findings with Grype ignores

I've dismissed a few alerts in the security/code scanning alerts page.

But whenever the scan action is executed it detects these vulnerabilities as being new and fails the check under `Code scanning results`

The job has the following permissions:

``` yaml
permissions:
security-events: write
```

And I'm running the scan action like this:

``` yaml
- name: Scan image
id: scan
uses: anchore/scan-action@v3
with:
image: ${{ steps.meta.outputs.tags }}
fail-build: false
severity-cutoff: "critical"
acs-report-enable: true
```

Any ideas on why it's reporting the dismissed (and already existing) alerts as new in the pr checks?

Start with the anchore/scan-action@v3 entry point and the workflow configuration shown in the issue, then trace how Grype results are submitted to GitHub Code scanning. Compare dismissed alerts with the action's handling of existing findings. Done means dismissed findings are not reported as new vulnerabilities in pull-request checks, while genuinely new findings remain visible.

Written by the indexing model from the issue text.