fix: add an unreachable return, to test signal termination

src/signal-termination.ts

@@ -94,6 +94,7 @@ export class TermSignals {
     }
     if (code !== undefined) {
       process.exit(code)
+      return // eslint-disable-line no-unreachable
     }
     throw new Error('Unable to terminate parent process successfully')
   }

test/signal-termination.spec.ts

@@ -71,6 +71,7 @@ describe('signal-termination', (): void => {
 
       it('should call exit method on parent process if no signal provided', (): void => {
         term._terminateProcess(0)
+        // We here test code that in reality is unreachable.
         assert.equal(exitStub.callCount, 1)
       })