fix: allow package pin contains - & _ chars

[dungdm93]

contents:
  keyring:
    - https://packages.wolfi.dev/os/wolfi-signing.rsa.pub
  repositories:
    - "@foo-bar https://packages.wolfi.dev/os"
  packages:
    - wolfi-baselayout@foo-bar
    - ca-certificates-bundle@foo-bar
    - tzdata@foo-bar
    - busybox@foo-bar

work-dir: /home/nonroot

accounts:
  run-as: nonroot
  groups:
    - groupname: nonroot
      gid: 65532
  users:
    - username: nonroot
      uid: 65532
      gid: 65532

cmd: "/bin/sh"

archs:
  - amd64

When building this image, I got following error:

❯ apko build apko.yaml foobar:123 foobar.tar.gz
...
2024/04/11 12:28:56 [DEBUG] HEAD https://packages.wolfi.dev/os/x86_64/APKINDEX.tar.gz
2024/04/11 12:28:56 [DEBUG] GET https://packages.wolfi.dev/os/x86_64/APKINDEX.tar.gz
Error: failed to build layer image for "amd64": installing apk packages: error getting package dependencies: could not find package, alias or a package that provides busybox@foo-bar in indexes
2024/04/11 12:29:01 error during command execution: failed to build layer image for "amd64": installing apk packages: error getting package dependencies: could not find package, alias or a package that provides busybox@foo-bar in indexes

As u can see, repository index is retrieved successfully, however, apko could not resolve packages because repository tag contains - character.