chore(helm/loki): Update helm CI workflow to fetch full history and PR ref

[site0801]

What this PR does / why we need it: I confirmed that super-linter at https://github.com/grafana/loki/pull/14838 is not able to ref the commit sha of PRs by external Contributors. Therefore, in this PR, I will include the target branch in the checkout before executing super-linter.

Which issue(s) this PR fixes: Fixes #

Special notes for your reviewer:

Checklist

• [ ] Reviewed the CONTRIBUTING.md guide (required)
• [ ] Documentation added
• [ ] Tests updated
• [ ] Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• [ ] Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• [ ] If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[site0801]

@trevorwhitney fixed it on https://github.com/grafana/loki/pull/15001! This PR seems unnecessary, so I'll close it.

[trevorwhitney]

ahh, thank you for the fix anyway!