Action fails on Node 24 default runner: "(0 , util_1.isNullOrUndefined) is not a function

### Describe the bug
The action crashes with a TypeError when GitHub Actions runners default to Node 24,
which is now the standard runtime since GitHub's Node 20 deprecation rollout.

Error:
Error: (0 , util_1.isNullOrUndefined) is not a function

This happens because `util.isNullOrUndefined` was removed in Node 24, and the
action's bundled dependencies still call it.

### To Reproduce
1. Use a GitHub Actions runner defaulting to Node 24 (current default as of mid-2026)
2. Run the action with a standard load test config:

- name: Run Azure Load Test
uses: azure/load-testing@v1.2.5
with:
loadTestConfigFile: loadtest-config.yaml
loadTestResource:
resourceGroup:
waitForCompletion: true
env:
USRNAME: ***
PASSWORD: ***
TEST_ID_CONFIG:

3. Observe the crash immediately on action startup

### Expected behavior
The action should run successfully on Node 24, matching the runner's default.

### Workaround
Setting ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true in the step's env forces
the runner back to Node 20, which avoids the crash — but this is only a temporary
option since GitHub is fully removing Node 20 support later in 2026:
https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

### Versions tested
- v1.2.1 — fails
- v1.2.5 (latest) — fails identically

### Environment
- GitHub-hosted runner (ubuntu-latest)
- Node 24 (runner default)