chore: set gitlab reference back to main branch (#2035)

# What does this PR do?

Set gitlab reference back to main branch

Author: hoolioh

.gitlab-ci.yml

@@ -2,7 +2,7 @@ variables:
   # These are gitlab variables so that it's easier to do a manual deploy
   # If these are set witih value and description, then it gives you UI elements
   DOWNSTREAM_BRANCH:
-    value: "julio/bump-msrv"
+    value: "main"
     description: "downstream jobs are triggered on this branch"
 
 include: