Updated promtail git tag

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/apps/sandbox/promtail/-/blob/6.8.1-bb.0/CHANGELOG.md

Package MR

https://repo1.dso.mil/big-bang/apps/sandbox/promtail/-/merge_requests/23

For Issue

Closes https://repo1.dso.mil/big-bang/apps/sandbox/promtail/-/issues/15