Update CONTRIB_REPO_SHA for misc too

Author: xrmx

.github/workflows/misc_0.yml

@@ -11,7 +11,7 @@ on:
 
 env:
   CORE_REPO_SHA: main
-  CONTRIB_REPO_SHA: main
+  CONTRIB_REPO_SHA: opentelemetrybot/prepare-release-1.29.0-0.50b0
   PIP_EXISTS_ACTION: w
 
 jobs: