fix linting

Author: joelharkes

__fixtures__/core.ts

@@ -11,4 +11,4 @@ export const setFailed = jest.fn<typeof core.setFailed>();
 export const warning = jest.fn<typeof core.warning>();
 export const startGroup = jest.fn<typeof core.startGroup>();
 export const endGroup = jest.fn<typeof core.endGroup>();
-export const isDebug = jest.fn<typeof core.isDebug>();
+export const isDebug = jest.fn<typeof core.isDebug>();