Update docker.io/library/nginx Docker tag to v1.26 (open-telemetry#32754

)

[![Mend
Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| docker.io/library/nginx | final | minor | `1.25` -> `1.26` |

---

> [!WARNING]
> Some dependencies could not be looked up. Check the Dependency
Dashboard for more information.

---

### Configuration

📅 **Schedule**: Branch creation - "on tuesday" (UTC), Automerge - At any
time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR has been generated by [Mend
Renovate](https://www.mend.io/free-developer-tools/renovate/). View
repository job log
[here](https://developer.mend.io/github/open-telemetry/opentelemetry-collector-contrib).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNy4zMjEuMiIsInVwZGF0ZWRJblZlciI6IjM3LjMzMS4wIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJkZXBlbmRlbmNpZXMiLCJyZW5vdmF0ZWJvdCJdfQ==-->

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Alex Boten <[email protected]>

receiver/nginxreceiver/testdata/integration/Dockerfile.nginx

@@ -1,4 +1,4 @@
-FROM docker.io/library/nginx:1.25
+FROM docker.io/library/nginx:1.26
 
 COPY default.conf /etc/nginx/conf.d/default.conf
 RUN \