chore: rename spec_test.rs => spec_tests.rs

[arendjr]

Summary

Some crates have spec_test.rs for running an individual test case, and a spec_tests.rs for running them all. This makes sense. What didn't make sense is that both biome_service and biome_module_graph had a spec_test.rs that contained multiple test cases. Other crates that only have a single file (everywhere that isn't parser or formatter crates, basically) all call the file spec_tests.rs. It annoyed me, because it messes with my Go To File command.

Test Plan

CI should remain green.