main url is text/html but package is trying to read json

Hi,

I am having issues using the package right from the beginning.

When I do the simplest test, I get an error :

> ```R
> # testing melodi's get_catalog method
> > melodi::get_catalog()
>
> Request all catalog : https://api.insee.fr/melodi/catalog/all
> Error in `httr2::resp_body_json()`:
> ! Unexpected content type "text/html".
> • Expecting type "application/json" or suffix "json".
> ```

so I backtrace it, and get :
> ```R
> > rlang::last_trace()
>
>
> Error in `httr2::resp_body_json()`:
> ! Unexpected content type "text/html".
> • Expecting type "application/json" or suffix "json".
> ---
> Backtrace:
> ▆
> 1. └─melodi::get_catalog()
> 2. └─httr2::resp_body_json(httr2::req_perform(httr2::request(url)), simplifyVector = TRUE)
> ```
This shows the package is using `httr2::resp_body_json` to something of type `text/html`. And indeed :

> ```R
> # testing url content type
> > httr2::resp_content_type(httr2::req_perform(httr2::request("https://api.insee.fr/catalog/all")))
> [1] "text/html"
> ```

It would be greatly appreciated to put some tests in this package so this does not happen on futur commits :)

Also, a quick fix would be great; probably have the package read the html, parse the content and translate it to json; but that being tried with :

> ```R
> # testing parsing xml to json so I can later parse the json
> > jsonlite::toJSON(
> xml2::read_xml(
> httr2::resp_body_string(
> httr2::req_perform(
> httr2::request("https://api.insee.fr/melodi/catalog/all")
> )
> )
> ),
> auto_unbox = TRUE,
> pretty = TRUE
> )
> ```

I get the error:

> ```R
> Erreur dans read_xml.raw(charToRaw(enc2utf8(x)), "UTF-8", ..., as_html = as_html, :
> Opening and ending tag mismatch: link line 12 and head [76]
> 5. read_xml.raw(charToRaw(enc2utf8(x)), "UTF-8", ..., as_html = as_html, options = options)
> 4. read_xml.character(httr2::resp_body_string(httr2::req_perform(httr2::request("https://api.insee.fr/melodi/catalog/all"))))
> 3. xml2::read_xml(httr2::resp_body_string(httr2::req_perform(httr2::request("https://api.insee.fr/melodi/catalog/all"))))
> 2. force(x)
> 1. jsonlite::toJSON(xml2::read_xml(httr2::resp_body_string(httr2::req_perform(httr2::request("https://api.insee.fr/melodi/catalog/all")))), auto_unbox = TRUE, pretty = TRUE)
> ```

which means something's off with the xml.

Maybe the xml should have some style information as seen from this screenshot