upgrade version nginxinc/nginx-unprivileged to 1.23 (#8984)

**What this PR does / why we need it**:

This PR upgrade nginxinc/nginx-unprivileged to 1.23

**Which issue(s) this PR fixes**:
Fixes #<issue number>

**Special notes for your reviewer**:

**Checklist**
- [x] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [ ] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/upgrading/_index.md`

Co-authored-by: Travis Patterson <travis.patterson@grafana.com>

docs/sources/installation/helm/reference.md

@@ -1067,7 +1067,7 @@ null
 			<td>string</td>
 			<td>The gateway image tag</td>
 			<td><pre lang="json">
-"1.19-alpine"
+"1.23-alpine"
 </pre>
 </td>
 		</tr>

production/helm/loki/values.yaml

@@ -1200,7 +1200,7 @@ gateway:
     # -- The gateway image repository
     repository: nginxinc/nginx-unprivileged
     # -- The gateway image tag
-    tag: 1.19-alpine
+    tag: 1.23-alpine
     # -- Overrides the gateway image tag with an image digest
     digest: null
     # -- The gateway image pull policy