MAINT: cleanup all `from_name` usage in tests

We should try to limit the unnecessary use of `SkyCoord.from_name` in the tests and just use baked in numbers for coordinates instead. That would remove some unnecessary extra calls to upstream that we don't need to test for (e.g. astropy should have enough coverage to ensure `from_name` just works).

Narrative docs is different IMO as the `from_name` is a really nice end user functionality, so we can keep promoting its usage.

Search the test suite for SkyCoord.from_name usage and identify calls that only obtain fixed coordinates for tests. Replace those test-only lookups with baked-in coordinate numbers, while leaving narrative documentation examples unchanged. Run the affected tests and confirm they no longer make unnecessary upstream coordinate-service calls.

Written by the indexing model from the issue text.