Generated migrations should use tuples instead of lists

[Daniel Quinn]

When running makemigrations, the typical output contains a Migration class with at least two attributes: dependencies and operations, both of which are mutable lists rather than immutable tuples. This upsets my linter (​ruff) which I think rightly ​complains that we've got a class here with mutable default values:

error[RUF012]: Mutable default value for class attribute
  --> plugins/generic_to_clickhouse/migrations/0001_initial.py:13:20
   |
11 |     initial = True
12 |
13 |     dependencies = []
   |                    ^^
14 |
15 |     operations = (
   |
help: Consider initializing in `__init__` or annotating with `typing.ClassVar`

Digging through the ​source, I see that this is just the result of a hard-coded template using [ instead of (, so I have to assume that a fix would be pretty straightforward.

So unless there's a reason we want these values to be mutable, I'm happy to do this work. I just don't want to do the work and have it rejected for unforseen reasons.