Exec format error on arm64 based runners

Hi,

When using an arm64 based runner, I get an exec format error when installing:

```
install:
runs-on: runs-on=${{ github.run_id }}/runner=2cpu-linux-arm64
steps:
- uses: carvel-dev/setup-action@v2
with:
only: imgpkg, kapp, kbld, imgpkg, vendir, ytt
token: ${{ secrets.token }}
- shell: bash
run: |
imgpkg version
kapp version
kbld version
vendir version
ytt version
```

It starts downloading the amd64 releases:

```
Installing imgpkg:latest, kapp:latest, kbld:latest, imgpkg:latest, vendir:latest, ytt:latest
Downloading ytt v0.52.0 from https://github.com/carvel-dev/ytt/releases/download/v0.52.0/ytt-linux-amd64
Downloading kbld v0.46.0 from https://github.com/carvel-dev/kbld/releases/download/v0.46.0/kbld-linux-amd64
Downloading imgpkg v0.46.1 from https://github.com/carvel-dev/imgpkg/releases/download/v0.46.1/imgpkg-linux-amd64
Downloading kapp v0.64.2 from https://github.com/carvel-dev/kapp/releases/download/v0.64.2/kapp-linux-amd64
Downloading imgpkg v0.46.1 from https://github.com/carvel-dev/imgpkg/releases/download/v0.46.1/imgpkg-linux-amd64
Downloading vendir v0.44.0 from https://github.com/carvel-dev/vendir/releases/download/v0.44.0/vendir-linux-amd64
✅ Verified checksum: "90e8d123d5e33ab13b849997bdb05626fa7f2384120d87a29eebd56490105ca9 ./kbld-linux-amd64"
✅ Verified checksum: "4c222403a9a2d54d8bb0e0ca46f699ee4040a2bddd5ab3b6354efd2c85d3209f ./ytt-linux-amd64"
✅ Verified checksum: "1bc6b735dbdd940a5c78661781f937090bd5fbc89172f01e600ee91fe122edbe ./imgpkg-linux-amd64"
✅ Verified checksum: "1bc6b735dbdd940a5c78661781f937090bd5fbc89172f01e600ee91fe122edbe ./imgpkg-linux-amd64"
✅ Verified checksum: "a2befbb9dd4f174aac7a34fe0bd50b1e5dc356dadaed0183a24b817f2fd1d094 ./vendir-linux-amd64"
```

```
/opt/hostedtoolcache/imgpkg/0.46.1/arm64/imgpkg: cannot execute binary file: Exec format error
```

Would be great if it could auto-detect the architecture and download the appropriate binary. Or allow us to specify arm64