[llvm-branch-commits] [CI] Use Github Native Groups in monolithic-* scripts (PR #143481)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/143481

This patch updates monolithic-linux.sh and monolithic-windows.sh to emit
expandable groups in the Github logs. The syntax this replaces
originally worked to produce the same functionality on Buildkite, but
Github uses a different syntax.

https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/workflow-commands-for-github-actions#grouping-log-lines