[flang-rt] Update `test_flang` in CI to use `flang-rt` as one of the projects.#135260

DanielCChen wants to merge 2 commits intollvm:mainllvm/llvm-project:mainfrom

DanielCChen:daniel_ci_flang_rtDanielCChen/llvm-project:daniel_ci_flang_rtCopy head branch name to clipboard