fix(Ash.Generator): Replace calls to create and create_many with generate and generate_many

[sevenseacat]

Currently, attempting to use Ash.Generator in tests will raise a warning:

Compiling 1 file (.ex)
    warning: Ash.Generator.create/1 is undefined or private
    │
  4 │   use Ash.Generator
    │   ~~~~~~~~~~~~~~~~~
    │
    └─ test/support/generator.ex:4: Tunez.Generator.create/1

    warning: Ash.Generator.create_many/1 is undefined or private. Did you mean:

          * generate_many/2

    │
  4 │   use Ash.Generator
    │   ~~~~~~~~~~~~~~~~~
    │
    └─ test/support/generator.ex:4: Tunez.Generator.create_many/1

[sevenseacat]

Though I'm not sure this is right - I'm still seeing errors when trying to use Ash.Generator 🤔

Compiling 31 files (.ex)
    error: imported Ash.Generator.generate/1 conflicts with local function
    │
  4 │   use Ash.Generator
    │   ^^^^^^^^^^^^^^^^^
    │
    └─ test/support/generator.ex:4: Tunez.Generator (module)

I don't have any generate functions in my code anywhere, so it must be coming from Ash.Generator internally?