settings.py: updated branch references to main

[mrshll1001]

Updated references to the default schema branch to 'main' in
anticipation of upcoming change in the schema repo

[michaelwood]

Just resolved some conflicts and rebased this. Thanks

[coveralls]

Pull Request Test Coverage Report for Build 14592207950

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 80.769%

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Totals
Change from base Build 14518847338:	0.0%
Covered Lines:	63
Relevant Lines:	78

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💛 - Coveralls