runs-on-slim does not allow multiple label selection

[zarenner]

Expected

runs-on-slim supports the same options for selecting based on label / group as runs-on.

Actual

Compiler errors with Expected format: "string"

runner-self-hosted-ubuntu2404-x64-host.md (1 error(s)):
  🟡 MEDIUM PRIORITY:
    1. .github/workflows/runner-self-hosted-ubuntu2404-x64-host.md:11:14: error: got array, want string. Expected format: "string"
 8 |   workflow_dispatch:
 9 | engine: copilot
10 | runs-on: [self-hosted, ubuntu2404, x64, host]
11 | runs-on-slim: [self-hosted, ubuntu2404, x64, host]