Configure `user.name` in `git_test.go` `run` method.
Configure `user.name` in `git_test.go` `run` method.

In my work to add downstream testing to `knative.dev/pkg` this test is failing with:

```
        git_test.go:216: ["error" git]: Error running git [commit --allow-empty -m Hello Moto]: exit status 128
            Author identity unknown

            *** Please tell me who you are.

            Run

              git config --global user.email "you@example.com"
              git config --global user.name "Your Name"

            to set your account's default identity.
            Omit --global to set the identity only in this repository.

            fatal: empty ident name (for <tester@tekton.dev>) not allowed
```

Ref: https://github.com/knative/pkg/pull/2233/checks?check_run_id=3423565615#step:6:528

Tekton already configures `user.email`, but it seems to reject this on Actions without `user.name` as well.

tektoncd/pipeline,tektoncd/pipeline