Thanks for the bug report. I will have a look at this, but I believe there is an issue with an index in your database and a recent migration attempts to fix that, but some issues cannot be fixed without a human intervention.
I believe the commit that introduced the migration that fails is this one:
You can try pinning your Discourse instance to the previous version which is commit 690e2f15ab9549486aaa6750e1093c1336bf17f2. Edit your app.yml file and set the version key under params. Make sure to uncomment that key too!
Then, everything should start and you should be able to remove the duplicated vuejs tag, but that might have some unwanted effects if the duplicated tag is in use. We will try to find a better solution, but this should work until then.