Replace assert.Fail with assert.FailNow (#27578)

assert.Fail() will continue to execute the code while assert.FailNow()
not. I thought those uses of assert.Fail() should exit immediately.
PS: perhaps it's a good idea to use
[require](https://pkg.go.dev/github.com/stretchr/testify/require)
somewhere because the assert package's default behavior does not exit
when an error occurs, which makes it difficult to find the root error
reason.

tests/integration/api_packages_nuget_test.go

@@ -326,7 +326,7 @@ AAAjQmxvYgAAAGm7ENm9SGxMtAFVvPUsPJTF6PbtAAAAAFcVogEJAAAAAQAAAA==`)
 					assert.Equal(t, nuget_module.PropertySymbolID, pps[0].Name)
 					assert.Equal(t, symbolID, pps[0].Value)
 				default:
-					assert.Fail(t, "unexpected file: %v", pf.Name)
+					assert.FailNow(t, "unexpected file: %v", pf.Name)
 				}
 			}