[CI] Minor fixes in dispatch_job.py

1. Using $ in python f-strings that will get interpreted by bash creates bash
  variables that then do not map to anything.
2. Move the step annotation back to where it was. Otherwise the timestamps show
  up before the annotation and it doesn't get interpeted correctly.

Author: boomanaiden154

zorg/buildbot/builders/annotated/premerge/dispatch_job.py

@@ -59,10 +59,9 @@ def start_build_linux(commit_sha: str, k8s_client) -> str:
     """Starts a pod to build/test on Linux at the specified SHA."""
     pod_name = f"build-{commit_sha}"
     commands = [
-        'echo "@@@BUILD_STEP Cloning Repository@@@"',
         "git clone --depth 100 https://github.com/llvm/llvm-project",
         "cd llvm-project",
-        f"git checkout ${commit_sha}",
+        f"git checkout {commit_sha}",
         "export CC=clang",
         "export CXX=clang++",
         "export POSTCOMMIT_CI=1",
@@ -193,6 +192,7 @@ def main(commit_sha: str, platform: str):
     namespace = PLATFORM_TO_NAMESPACE[platform]
     latest_time = datetime.datetime.min
     v1_api = kubernetes.client.CoreV1Api()
+    print("@@@BUILD_STEP Build/Test@@@")
     while True:
         try:
             pod_finished, latest_time = print_logs(