Update part4b.md

Added missing word 'if' in line 1142

Author: mishrasur7

src/content/4/en/part4b.md

@@ -1139,7 +1139,7 @@ describe('viewing a specific note', () => {
       .expect(404)
   })
 
-  test('fails with statuscode 400 id is invalid', async () => {
+  test('fails with statuscode 400 if id is invalid', async () => {
     const invalidId = '5a3d5da59070081a82a3445'
 
     await api