Fix stale perlin test that pins dropped-coords behavior (main is red)

[brendancol]

main is currently red on the run (..., 3.14) checks. The matrix runs fail-fast, so when the ubuntu 3.14 job fails the macOS/Windows/3.14t jobs report as canceled, but there is only one real failure:

FAILED xrspatial/tests/test_perlin.py::test_perlin_drops_input_coords
AssertionError: assert 'lat' not in Coordinates: ...

This is a merge race between two perlin PRs:

• Add perlin test coverage: params, degenerate shapes, metadata #3472 added test_perlin_drops_input_coords, pinning the old behavior where perlin() dropped input coordinates. Its comment says to "Flip this to assert the coords ARE preserved once that is fixed."
• perlin: preserve input x/y coordinates on the output #3470 then changed perlin() to preserve the caller's x/y coordinates, but did not update the pinning test.

They merged in an order that left the test asserting behavior the code no longer has.

This flips the test to match the shipped behavior: it now asserts the coordinates are preserved and equal to the input, and is renamed test_perlin_preserves_input_coords. No source changes; perlin() already does the right thing.

Test plan:

• pytest xrspatial/tests/test_perlin.py — 31 passed

[brendancol]

Superseded by #3489, which already fixed the same stale perlin coords test on main (parallel duplicate). Closing as redundant.