Aurora Serverless alter table Error 1114 table is full
On the AWS Forums, LawrenceAtAWS said,


  the amount of temporary storage space associated with Serverless increases linearly with the number of associated ACUs. If you're having issues running out of temporary storage space for large table mutations, you could temporarily scale the cluster up to a larger number of ACUs and then run the modify statement. This should increase the associated temporary storage an allow the statement to succeed.


The way to achieve this with the CLI is
  aws rds modify-current-db-cluster-capacity --db-cluster-identifier sample-cluster --capacity 64