Update linkchecker.yml (#1536)

### Proposed changes

Need to add a newly invalid 3rd party URL to the linkchecker ignore
list. This is only used as an example and not an actual product link for
users. (Similar to www.example.com)


### Checklist

Before creating a PR, run through this checklist and mark each step as
complete.

- [ ] I have read the
[`CONTRIBUTING`](https://github.com/nginxinc/docs/blob/main/CONTRIBUTING.md)
document
- [ ] I have viewed my changes in the documentation Deploy Preview
- [ ] My PR is targeting the correct branch:
  - main: content that can be released immediately
- product release branch: content that should be held for a future
release
- [ ] I have updated any relevant supporting documentation
([`README.md`](https://github.com/nginxinc/docs/blob/main/README.md) and
the
[`CHANGELOG.md`](https://github.com/nginxinc/docs/blob/main/CHANGELOG.md))
- [ ] I have followed the [conventional commits
guidelines](https://www.conventionalcommits.org/en/v1.0.0/#summary) for
all commits on my branch

When you're ready to merge a PR, run through this checklist and mark
each step as complete.

- [ ] Review the doc for spelling errors.
- [ ] Verify that all links in the doc work.
- [ ] Verify that the doc follows the appropriate content template.
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Author: nginx-aoife

.github/workflows/linkchecker.yml

@@ -31,6 +31,7 @@ env:
     --ignore-url ^https://lightstep.com --ignore-url ^https://www.owasp.org/ --ignore-url ^https://www.maxmind.com --ignore-url ^https://www.splunk.com/
     --ignore-url ^https://oauth2.googleapis.com --ignore-url ^https://openidconnect.googleapis.com --ignore-url ^https://www.base64url.com/
     --ignore-url ^https://go.googlesource.com/ --ignore-url ^https://go.googlesource.com/sync --ignore-url ^https://linkerd.io/2.13/
+    --ignore-url ^http://www.redirectpage.com/
     --ignore-url ^https://\([a-zA-Z0-9-]+\).nginx.com/nginx-ingress-controller/css
     --ignore-url ^https://\([a-zA-Z0-9-]+\).nginx.com/nginxaas/azure/css
     --ignore-url ^https://\([a-zA-Z0-9-]+\).nginx.com/nginx-gateway-fabric/css
@@ -107,4 +108,4 @@ jobs:
         with:
           timeout_minutes: 10
           max_attempts: 3
-          command: ${{ env.cmd }}
+          command: ${{ env.cmd }}