Override repositories used by pak

[walkowif]

Without overriding these repositories, we have the following output of the second Show lockfile step of setup-r-dependencies (cli shown as an example) (example job):

"metadata": {
  "RemoteType": "standard",

  "RemotePkgRef": "cli",
  "RemoteRef": "cli",
  "RemoteRepos": "https://cloud.r-project.org/",
  "RemotePkgPlatform": "source",
  "RemoteSha": "3.6.3"
},
"sources": ["https://cloud.r-project.org/src/contrib/cli_3.6.3.tar.gz", "https://cloud.r-project.org/src/contrib/Archive/cli/cli_3.6.3.tar.gz"],
"target": "src/contrib/cli_3.6.3.tar.gz",
"platform": "source",

When we override the repositories using the method from this PR, we have the following output of the second Show lockfile step of setup-r-dependencies (cli shown as an example) (example job):

"metadata": {
    "RemoteType": "standard",
    "RemotePkgRef": "cli",
    "RemoteRef": "cli",
    "RemoteRepos": "https://packagemanager.posit.co/cran/__linux__/jammy/latest",
    "RemotePkgPlatform": "x86_64-pc-linux-gnu-ubuntu-22.04",
    "RemoteSha": "3.6.3"
  },
"sources": ["https://packagemanager.posit.co/cran/__linux__/jammy/latest/src/contrib/cli_3.6.3.tar.gz"],
"target": "src/contrib/x86_64-pc-linux-gnu-ubuntu-22.04/4.4/cli_3.6.3.tar.gz",
"platform": "x86_64-pc-linux-gnu-ubuntu-22.04",