accent marks should make animint2pages error

[tdhock]

github does not allow accent marks in repo names.

> animint2pages(viz, "2026-09-16-échantillons-pour-régression", chromote_sleep_seconds = 5)
Loading required namespace: gert
Loading required namespace: gh
Serving the directory /tmp/RtmpV5FP0m/file52ad4620dc7ed at http://127.0.0.1:3113
Looking up https credentials for https://github.com/tdhock/2026-09-16--chantillons-pour-r-gression.git
Transferred 3 of 3 objects...done!
[status] refs/heads/gh-pages: unchanged
[new]     fd8d9da61fd916586cf0 refs/remotes/origin/gh-pages
Looking up https credentials for https://github.com/tdhock/2026-09-16--chantillons-pour-r-gression.git
Transferred 683 of 683 objects...done!
[status] refs/heads/gh-pages: unchanged
[updated] fd8d9da61f..10c7f9192d refs/remotes/origin/gh-pages
Visualization will be available at https://tdhock.github.io/2026-09-16-échantillons-pour-régression
Deployment via GitHub Pages may take a few minutes...
$owner_repo
[1] "tdhock/2026-09-16-échantillons-pour-régression"

$local_clone
[1] "/tmp/RtmpV5FP0m/file52ad4492f7dfc"

$viz_url
[1] "https://tdhock.github.io/2026-09-16-échantillons-pour-régression"

$gh_pages_url
[1] "https://github.com/tdhock/2026-09-16-échantillons-pour-régression/tree/gh-pages"

this is problematic because the returned url is not valid.
https://tdhock.github.io/2026-09-16-échantillons-pour-régression

it should be https://tdhock.github.io/2026-09-16--chantillons-pour-r-gression/

we should stop with an error before creating the repo.