Docs building is broken - Read the docs project has it's default branch set to master instead of main

[CameronMackenzie99]

• What is the current behavior?
  The RTD project is currently not building documentation for the last 1 year and two months (see RTD builds). I believe this coincides with moving from master to main as the default git branch, and this change not being reflected in the RTD project configuration.
  Upon inspection of the latest build we can see it failed due to a missing .readthedocs.yaml file. This was fixed in Fix ReadTheDocs builds #1509 by @PabloAlexis611 , but as noted in that PR, the configuration of the RTD project has not been changed due to lack of access.

• What is the motivation to fix this bug?
  There have been fixes to various documentation error (e.g. in the tutorial) which have been merged, but not propagated to the latest doc site. This has created confusion with new issues being raised for already fixed docs issues, and means that the docs will become more outdated as new versions of graphene-django are released.

• What is the fix?
  Setting the default branch in the RTD project to main should get the docs generating again as expected. From the project view here the list of maintainers are:
  @syrusakbary
  @ekampf
  @ProjectCheshire
  @mvanlonden

Would one of you be able to update the configuration of the project to build off the main branch? I'm happy to test that the configuration works once this has been updated. Thanks!