fix: github actions versions and warnings (#639)

* fix: github actions versions and warnings

- [x] upgrade github/actions/cache GitHub Action to latest
 - this fixings the following warnings (example list [here](https://github.com/argoproj/gitops-engine/actions/runs/11885468091)):
   - Your workflow is using a version of actions/cache that is scheduled for deprecation, actions/cache@v2.1.6. Please update your workflow to use the latest version of actions/cache to avoid interruptions. Learn more: https://github.blog/changelog/2024-09-16-notice-of-upcoming-deprecations-and-changes-in-github-actions-services/
   - The `save-state` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
   - The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
- [x] update dependabot config
  - prefix PRs with `chore(deps)`
  - group non major version updates into 1 PR

Signed-off-by: jmeridth <jmeridth@gmail.com>

* fix: switch to SHA from tags

more secure, as tags are mutable

Signed-off-by: jmeridth <jmeridth@gmail.com>

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Signed-off-by: jmeridth <jmeridth@gmail.com>