ci: CI fails when enabling clipboard on the actions

[fox0430]

Caused by xvfb and clipboard on the github actions.

Log

  xvfb-run --auto-servernum nimble test --verbose -Y
  shell: /usr/bin/bash -e {0}
  env:
    NIM_VERSION: stable
    PATH: /home/runner/.nimble/bin:/home/linuxbrew/.linuxbrew/bin:/home/linuxbrew/.linuxbrew/sbin:/home/runner/.local/bin:/opt/pipx_bin:/home/runner/.cargo/bin:/home/runner/.config/composer/vendor/bin:/usr/local/.ghcup/bin:/home/runner/.dotnet/tools:/snap/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
    DISPLAY: :99.0
  Verifying dependencies for [email protected]
    Reading official package list

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  [OK] Case 5: if the current line end with and in Python
  [OK] Case 5: if the current line end with : in Python
Error: execution of an external program failed: '/home/runner/work/moe/moe/tests/teditor '
     Error: Execution failed with exit code 1
        ... Command: /home/runner/.nimble/bin/nim c --noNimblePath -d:NimblePkgVersion=0.4.0 --path:/home/runner/.nimble/pkgs/ncurses-1.0.2 --path:/home/runner/.nimble/pkgs/unicodedb-0.10.0 --path:/home/runner/.nimble/pkgs/parsetoml-0.6.0 -r --path:. /home/runner/work/moe/moe/tests/teditor
X connection to :99 broken (explicit kill or server shutdown).
Error: Process completed with exit code 1.