Verify failure of PipelineRun in TestGitPipelineRunFail

`TestGitPipelineRunFail` is test that is meant to verify that code
extraction fails with invalid inputs to the `Git` `PipelineResource`.

However, the test does not fail if the `PipelineRun` does not succeed.

In this change, we ensure that the `PipelineRun` fails in these
circumstances.

test/git_checkout_test.go

@@ -278,6 +278,8 @@ func TestGitPipelineRunFail(t *testing.T) {
 						}
 					}
 				}
+			} else {
+				t.Fatal("PipelineRun succeeded when should have failed")
 			}
 		})
 	}