Gene therapy refers to changing the genetic code of some or all of the cells of the organism getting the therapy.
The mRNA that is injected via a vaccine is just translated to protein by some of our cells.
There are no new genes being integrated into the DNA of any cell.
If these vaccines are doing "gene therapy" on your deltoid, then covid would be doing way more than just "gene therapy" all over your body, including your nervous system.
But neither is doing gene therapy.