Disabling GH Pages does not work when the github-pages environment still exists

[netomi]

For convenience reasons, the github-pages environment will be ignored by otterdog when it is not present in the configuration.
This normally works fine, however, when disabling GH Pages, the environment needs to be deleted first as otherwise the API call fails with:

[TRACE] 'DELETE' result = (422, {"message":"Deactivating GitHub pages for this repository is not allowed.","documentation_url":"https://docs.github.com/rest/pages/pages#delete-a-apiname-pages-site","status":"422"})

Thus we need to explicitly delete the github-pages environment when disabling GH Pages even if its not present in the configuration.