fixed ocs function for Group Folders app routes

[bigcat88]

Fixes #277 .

Changes proposed in this pull request:

• we use request.headers["Accept"] = "application/json" in addition of appending format=json to the query url(look below why).
• changed ocs_regexp to r"/ocs/v[12]\.php/|/apps/groupfolders/" until groupfolder app will fix it.

[bigcat88]

Note for future:
Nextcloud 30 does not respect Accept: application/json header when exception occurs and output xml, that's why I didn't remove request.url = request.url.copy_merge_params({"format": "json"}) line from _session.py

https://docs.nextcloud.com/server/latest/developer_manual/server/externalapi.html#output

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.13%. Comparing base (e56e324) to head (86ac367).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #279   +/-   ##
=======================================
  Coverage   94.13%   94.13%           
=======================================
  Files          48       48           
  Lines        5492     5494    +2     
=======================================
+ Hits         5170     5172    +2     
  Misses        322      322           

Files	Coverage Δ
nc_py_api/_session.py	96.47% <100.00%> (+0.02%)	⬆️

[bigcat88]

will merge this and looks like it is a good idea to make API for GroupFolders as it is pretty popular