Add our own variable names into the allowed words dictionary
If you include `--dot` in your CSpell options (as we [document here](https://project.pages.drupalcode.org/gitlab_templates/jobs/cspell/#hidden-files)) then I have found that some our own Gitlab Templates variables cause spelling errors, eg 'FLAGWORDS' in [this downstream cspell job](https://git.drupalcode.org/project/gitlab_templates_downstream/-/jobs/9056532#L70) Gitlab Templates has solved this by adding these names to our own project dictionary. But I would consider it to be a bug if you try to use any documented variable in your own pipeline and it immediately fails spelling. If we are providing these variables for use, then I suggest we should add the words into the allowed list for all Contrib. This can be done very easily in prepare-cspell.php as we [already do this kind of thing](https://git.drupalcode.org/project/gitlab_templates/-/blob/main/scripts/prepare-cspell.php#L129-142)
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