Bump to core-3.0.0, move to vitest, support ESM modules (#587)

__mocks__/@actions/core.ts

@@ -0,0 +1,9 @@
+import { vi } from "vitest"
+
+export const debug = vi.fn()
+export const getBooleanInput = vi.fn()
+export const getInput = vi.fn()
+export const notice = vi.fn()
+export const setFailed = vi.fn()
+export const setOutput = vi.fn()
+export const warning = vi.fn()