fix(cli-separator): negative value on a long text

[Mesteery]

When text is longer than 78 characters (with default length), rest is negative, which raises an error at repeat, making some commands unusable (when a long argument is given).

RangeError: Invalid count value
    at String.repeat (<anonymous>)
    at CLI.separator (C:\Users\me\AppData\Local\Volta\tools\image\packages\node-core-utils\node_modules\node-core-utils\lib\cli.js:133:22)
    at WPTUpdater.checkNeedsUpdate (C:\Users\me\AppData\Local\Volta\tools\image\packages\node-core-utils\node_modules\node-core-utils\lib\wpt\index.js:127:14)
    at WPTUpdater.update (C:\Users\me\AppData\Local\Volta\tools\image\packages\node-core-utils\node_modules\node-core-utils\lib\wpt\index.js:155:36)
    at main (C:\Users\me\AppData\Local\Volta\tools\image\packages\node-core-utils\node_modules\node-core-utils\components\git\wpt.js:78:19)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

[codecov]

Codecov Report

Merging #553 (d79b216) into main (f2f77dd) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #553   +/-   ##
=======================================
  Coverage   82.57%   82.57%           
=======================================
  Files          35       35           
  Lines        1750     1750           
=======================================
  Hits         1445     1445           
  Misses        305      305           

Impacted Files	Coverage Δ
lib/cli.js	88.73% <100.00%> (ø)

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