fix: remove invalid 'run' key from install-curl step in cmake workflow (#507)

# fix: remove invalid 'run' key from cmake workflow step

## Summary

The `test-ubuntu-curl` job in `.github/workflows/cmake.yml` has a step
with both `uses:` and `run:` keys, which is invalid in GitHub Actions (a
step must be one or the other). This causes the entire workflow to fail
immediately with 0 jobs — the root cause of the failure in [run
22914048955](https://github.com/launchdarkly/cpp-sdks/actions/runs/22914048955).

The invalid `run: sudo apt-get update && sudo apt-get install -y
libcurl4-openssl-dev` was added in PR #500 (commit 5b8bbee). It is also
redundant — the `.github/actions/install-curl` composite action already
runs `apt-get install libcurl4-openssl-dev` on Linux internally.

The fix simply removes the erroneous `run:` line.

## Review & Testing Checklist for Human

- [ ] Verify the [install-curl composite
action](https://github.com/launchdarkly/cpp-sdks/blob/main/.github/actions/install-curl/action.yml)
still handles Linux curl installation via `apt-get` (it does as of this
writing)
- [ ] After merging, confirm the `cmake-integration` workflow runs
successfully on `main` with all 6 jobs created

### Notes
- Requested by: @kinyoklion
- [Link to Devin
Session](https://app.devin.ai/sessions/8a014c6f323f4134a116aef51d57d9d3)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Fixes a GitHub Actions YAML syntax issue in CI; no production code
changes and behavior remains handled by the existing `install-curl`
composite action.
> 
> **Overview**
> Fixes the `cmake-integration` GitHub Actions workflow by removing an
invalid `run` command from the `test-ubuntu-curl` step that already
`uses` the `install-curl` composite action.
> 
> This prevents the workflow from failing to start due to an invalid
step definition, while keeping curl installation delegated to
`./.github/actions/install-curl`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
6d88ed6. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: kinyoklion

.github/workflows/cmake.yml

@@ -30,7 +30,6 @@ jobs:
       - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955
       - uses: ./.github/actions/install-curl
         id: install-curl
-        run: sudo apt-get update && sudo apt-get install -y libcurl4-openssl-dev
       - uses: ./.github/actions/cmake-test
         env:
           CURL_ROOT: ${{ steps.install-curl.outputs.CURL_ROOT }}