github-custom-runners does not support arrays

[FreeMasen]

According to the GHA docs

You can provide runs-on as:

• A single string
• A single variable containing a string
• An array of strings, variables containing strings, or a combination of both
• A key: value pair using the group or labels keys

If you specify an array of strings or variables, your workflow will execute on any runner that matches all of the specified runs-on values.

but currently using the following will fail

[build.github-custom-runners]
x86_64-unknown-linux-gnu = ["self-hosted", "linux", "x64", "gpu"]

will fail with the following output

cargo dist generate

  × failed to parse TOML
  ╰─▶ TOML parse error at line 20, column 28
         |
      20 | x86_64-unknown-linux-gnu = ["self-hosted", "linux", "x64", "gpu"]
         |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      data did not match any variant of untagged enum StringLikeOr
      
    ╭─[/Users/rfm/projects/changelog-builder/dist-workspace.toml:20:28]
 19 │ [dist.github-custom-runners]
 20 │ x86_64-unknown-linux-gnu = ["self-hosted", "linux", "x64", "gpu"]
    ·                            ──────────────────────────────────────
    ╰────