build: add GO_VERSION to workflows and update build image Dockerfile

[Kim-Yukyung]

What this PR does / why we need it

This PR propagates the GO_VERSION value into all GitHub workflows that rely on the Loki build image, ensuring that the workflows use the same Go toolchain version defined by the project. In addition, the loki-build-image Dockerfile is updated to reference the same Go version.

These changes improve build reproducibility and prevent version drift between the build image, local development environment, and CI workflows. Although the image tag itself is not bumped in this PR, the updates lay the groundwork for a consistent future build-image release.

Which issue(s) this PR fixes

Fixes #19818

Checklist

• [x] Reviewed the CONTRIBUTING.md guide (required)
• [ ] Documentation added
• [ ] Tests updated
• [x] 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

[CLAassistant]

All committers have signed the CLA.