Incorrect `source` value on installed packages

[zooba]

From #258 we see in the py list -f=json output that packages have been installed from Nuget (see url value) but they claim to have come from the bundled index (see source value).

This shouldn't be possible, so it probably means we're setting the source incorrectly.

    {
      "schema": 1,
      "id": "pythoncore-3.11-arm64",
      "sort-version": "3.11.9",
      "company": "PythonCore",
      "tag": "3.11.9-arm64",
      "install-for": [
        "3.11.9-arm64",
        "3.11-arm64",
        "3-arm64"
      ],
      "run-for": [
        {
          "tag": "3.11-arm64",
          "target": "python.exe"
        },
        {
          "tag": "3-arm64",
          "target": "python.exe"
        }
      ],
      "alias": [
        {
          "name": "python3.11-arm64.exe",
          "target": "python.exe"
        },
        {
          "name": "python3-arm64.exe",
          "target": "python.exe"
        },
        {
          "name": "pythonw3.11-arm64.exe",
          "target": "pythonw.exe",
          "windowed": 1
        },
        {
          "name": "pythonw3-arm64.exe",
          "target": "pythonw.exe",
          "windowed": 1
        }
      ],
      "shortcuts": [
        {
          "kind": "pep514",
          "Key": "PythonCore\\3.11-arm64",
          "DisplayName": "Python 3.11.9 (ARM64)",
          "SupportUrl": "https://www.python.org/",
          "SysArchitecture": "64bit",
          "SysVersion": "3.11",
          "Version": "3.11.9",
          "InstallPath": {
            "": "%PREFIX%",
            "ExecutablePath": "%PREFIX%python.exe",
            "WindowedExecutablePath": "%PREFIX%pythonw.exe"
          },
          "Help": {
            "Online Python Documentation": {
              "": "https://docs.python.org/3.11/"
            }
          }
        },
        {
          "kind": "start",
          "Name": "Python 3.11 (ARM64)",
          "Items": [
            {
              "Name": "Python 3.11 (ARM64)",
              "Target": "%PREFIX%python.exe",
              "Icon": "%PREFIX%python.exe"
            },
            {
              "Name": "Python 3.11 Documentation",
              "Icon": "%SystemRoot%\\System32\\SHELL32.dll",
              "IconIndex": 13,
              "Target": "https://docs.python.org/3.11/"
            }
          ]
        }
      ],
      "displayName": "Python 3.11.9 (ARM64)",
      "executable": "C:\\Users\\bagpuss\\AppData\\Local\\Python\\pythoncore-3.11-arm64\\python.exe",
      "url": "https://api.nuget.org/v3-flatcontainer/pythonarm64/3.11.9/pythonarm64.3.11.9.nupkg",
      "__original-shortcuts": [
        {
          "kind": "pep514",
          "Key": "PythonCore\\3.11-arm64",
          "DisplayName": "Python 3.11.9 (ARM64)",
          "SupportUrl": "https://www.python.org/",
          "SysArchitecture": "64bit",
          "SysVersion": "3.11",
          "Version": "3.11.9",
          "InstallPath": {
            "": "%PREFIX%",
            "ExecutablePath": "%PREFIX%python.exe",
            "WindowedExecutablePath": "%PREFIX%pythonw.exe"
          },
          "Help": {
            "Online Python Documentation": {
              "": "https://docs.python.org/3.11/"
            }
          }
        },
        {
          "kind": "start",
          "Name": "Python 3.11 (ARM64)",
          "Items": [
            {
              "Name": "Python 3.11 (ARM64)",
              "Target": "%PREFIX%python.exe",
              "Icon": "%PREFIX%python.exe"
            },
            {
              "Name": "Python 3.11 Documentation",
              "Icon": "%SystemRoot%\\System32\\SHELL32.dll",
              "IconIndex": 13,
              "Target": "https://docs.python.org/3.11/"
            }
          ]
        }
      ],
      "source": "file:///C:/Program%20Files/WindowsApps/PythonSoftwareFoundation.PythonManager_0.1.0.164_x64__7qnp2ymwnadz2/bundled/index.json",
      "display-name": "Python 3.11.9 (ARM64)",
      "prefix": "C:\\Users\\bagpuss\\AppData\\Local\\Python\\pythoncore-3.11-arm64"
    }