Force cloning or pull of repo on each run of envbuilder

When using envbuilder and restarting my workspace I nearly always want a fresh copy of the repo, but when using a pvc similar to this [example template](https://github.com/coder/coder/blob/main/examples/templates/devcontainer-kubernetes/main.tf) I envbuilder simply finds the existing repo, prints:

```
#1: 📦 Cloning MY_REPO...
#1: 📦 The repository already exists! [5.29944ms]
```

I see no way to force envbuilder to either clone it each time or, preferably, run a git pull to ensure the repo is fresh between rebuilds, but this would make the process more intuitive for our users.

Start by tracing the envbuilder repository setup path that emits the “repository already exists” message, using the linked Kubernetes template as context. Determine how a repeat run should refresh an existing repository, then verify that restarting a workspace produces the expected fresh repository state; the issue names no files or tests.

Written by the indexing model from the issue text.