[ARM] az bicep: fix installation check for concurrent usages

If `az` is called by multiple processes or threads the code has a race
condition. By simply allowing for the directory to exist, the same
behavior as before is achieved without failing in concurrent usages.

Author: marlamb

src/azure-cli/azure/cli/command_modules/resource/_bicep.py

@@ -122,8 +122,7 @@ def ensure_bicep_installation(cli_ctx, release_tag=None, target_platform=None, s
             return
 
     installation_dir = os.path.dirname(installation_path)
-    if not os.path.exists(installation_dir):
-        os.makedirs(installation_dir)
+    os.makedirs(installation_dir, exist_ok=True)
 
     try:
         release_tag = release_tag if release_tag else get_bicep_latest_release_tag()