Switch from -Z to -w
Switch from -Z to -w

The flag `-Z` (trailing space) is not available in all versions of `diff`, but `-w` (all space) is available.

When I run things on my macbook I hit:
```
e2e_test.go:107: diff: invalid option -- Z
diff: Try `diff --help' for more information.
```

Fixes: https://github.com/tektoncd/pipeline/issues/4177

tektoncd/pipeline,tektoncd/pipeline