docs: remove the negative refspec for version-3-4 (#8717)

Author: addetz

scripts/index-breaking-changes.sh

@@ -34,8 +34,7 @@ fi
 # Pull *only* version-* branches into refs/remotes/origin/, shallow, skip tags,
 # and explicitly exclude version-3-4 with a negative refspec.
 git fetch --prune --no-tags --depth=1 origin \
-  '+refs/heads/version-*:refs/remotes/origin/version-*' \
-  '^refs/heads/version-3-4'
+  '+refs/heads/version-*:refs/remotes/origin/version-*'
 
 # Get remote version branches (no locals, no HEAD), exclude version-3-4
 branches="$(