simplify tests where `Identity()` was needed as last transformation in a sequence

[LucaMarconato]

In a test for sequence transformations I had to add some Identity() transformations due to a limitation of _get_current_output_axes(). See here: https://github.com/scverse/spatialdata/blob/a9fb47776701498a5ecca5e3c5e56a02d59d1224/tests/transformations/test_transformations.py#L435

• [ ] verify that this is not needed anymore and drop the Identity() from the tests

[LucaMarconato]

I verified, the test is correct also when the last instances of Identity() are dropped, as expected. We need to make a small PR to remove them from the test.