I have had the same problem with two of my clients with the Sharepoint_config database.
I think the Sharepoint recommendation for that database is to have it in Full recovery mode. So the only way to control it's size is to take frequent log backups.
I have scheduled one every 10 mins but I avoid shrinking the log file since that will eventually lead to more autogrowth events.
I moved the log file to a new disk drive which has more space allocated. If I am correct, I have allocated 120 GB for the disk where the log file resides. I have seen the log file getting as much as 100 GB within a matter of minutes.
On one instance, I didn't have enough space to take log backups. Instead, I changed the database to simple recovery and shrinked log file. Then changed it back to full recovery and took a full backup.
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