Utilise file instead of stderr for integration tests

Windows for some reason is not properly making use of stderr so instead
we're going to write our result to a file explicitly

pkg/integration/tests/commit/commit.go

@@ -27,7 +27,7 @@ var Commit = NewIntegrationTest(NewIntegrationTestArgs{
 			PressPrimaryAction(). // stage file
 			Lines(
 				Contains("A  myfile").IsSelected(),
-				Contains("?? myfile2"),
+				Contains("?? myfile23"),
 			).
 			SelectNextItem().
 			PressPrimaryAction(). // stage other file