chore: trigger eks nightly when related files are updated (#366)

## Description
trigger the eks nightly tests on pull requests only when related files
are changed.

## Related Issue

Fixes #
<!-- or -->
Relates to #

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [x] Other (security config, docs update, etc)

## Checklist before merging

- [ ] Test, docs, adr added or updated as needed
- [ ] [Contributor Guide
Steps](https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md)(https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md#submitting-a-pull-request)
followed

Co-authored-by: Micah Nagel <micah.nagel@defenseunicorns.com>

.github/workflows/nightly-testing.yaml

@@ -3,6 +3,12 @@ name: Nightly Testing
 on:
   schedule:
     - cron: '0 6 * * *' # Runs at midnight Mountain every day
+  pull_request:
+    paths:
+      - tasks/iac.yaml
+      - .github/workflows/test-eks.yaml
+      - .github/bundles/*
+      - .github/test-infra/buckets-iac/*
 
 jobs:
   nightly-testing: